EXCRETORY SYSTEM
At the end of this chapter, students should be able to:
Identify and describe different types of excretory systems in plants and animals;
Explain the mechanisms of some of the excretory organs and relate structure to functions.

Definition of excretion
Excretion is the removal of waste products of metabolism which are harmful or would in time interfere with normal functions of organisms.
Note: excretion is not the same as egestion and secretion. Egestion is the removal of solid undigested food substances which are not by-products of metabolism, e.g. The removal of faeces from anus. Secretion on the other hand is the production of useful substances in the body by some special cells, e.g. Production of enzymes and hormones.

Importance of Excretion
We need to eliminate waste metabolic substances because of the following reasons:
The excretory products are harmful/toxic to the body hence, they need to be removed;
Some metabolic substances are poisonous whenever they accumulate in the body;
Excretion maintains water balance in the body;
Excretion maintains salt balance in the body;
Waste products when not removed can interfere with normal metabolic activities of the body.




MECHANISM OF EXCRETION IN SOME ORGANISMS

FLATWORMS










The excretory system consists of two longitudinal canals with network of ducts (tubules). The ducts branch to all parts of the body and end up in flame like cells.
The waste products e.g. water, ammonia and Carbon dioxide diffuse from the surrounding cells into the flame cells. With the aid of the flagella/ or cilia, which suck the excretory products into the funnel, the fluid containing the waste products is propelled/driven into the tubules. And finally they are eventually removed at the exterior.
Note: another major function of the flame cells is the regulation of the water content of the animal i.e. Osmoregulation.

EARTHWORM










Nephridium is the excretory organ in earthworm. Each Nephridium consists of a flattened funnel-like structure with two lips called the nephrostome. The earthworm excretes urea and guanin. The beating of the cilia of the nephrostome draws coelomic fluid. During this process of drawing fluid, salts and other useful substances are reabsorbed through the walls of the tubes. The unabsorbed substances, including water, are collected in the muscular tubes as urine. The excretory pore relaxes to allow the urine to escape to the exterior. While Carbon dioxide are removed through the moist body surface during gaseous exchange.

CRUSTACEANS











The excretory organ in crustacean are the green glands. Each gland consists of five parts: a small end sac, the green gland, flattened disc called the labyrinth, the Nephridium canal, and the urinary bladder.
How green glands perform excretion in crustacean

The green gland extracts metabolic wastes from the blood. During this process of extraction, water and dissolved salts pass into the end sac by filtration. Nitrogenous waste materials pass into the labyrinth. Selective reabsorption of salts and glucose takes place at the nephridial canal according to the needs of the animal. Urine is formed. The urine formed is hypotonic to the blood, and is collected in the urinary bladder and removed by the muscular contraction of the walls of the bladder, and discharged to the outside through the pair of excretory pores located at the base of the antennae.

Note: some of the crustacean's waste Carbon dioxide is excreted through the gills and some, together with calcium, is known to be used by crayfish to strengthen its exoskeleton.

INSECTS












The excretory organs of insects are the Malpighian tubules. They are found between the midgut and the rectum; each tubule consists of two parts:  the distal end (free and closed end, floating in the haemocoel) and the proximal end (opens into the gut).

MECHANISM OF EXCRETION IN INSECTS.
When nitrogenous waste products and water are liberated into the haemocoel, they are absorbed at the distal end of the malpighian tubules. At the distal end, urates of potassium and sodium are extracted from the blood. The alkaline contents at the proximal end become acidic due to the addition of carbon dioxide, hence uric acid is precipitated and the potassium and sodium ions are re-absorbed as bicarbonate. The uric acid is passed into the ileum, from where it is passed out mixed with faeces. More water is re-absorbed at the rectum. The uric acid, mixed with faeces, is thus expelled as more or less dry material.
Note:
1. Excretion by storage: This is an uncommon form of excretion in insects, which involves storing up of uric acid in special fat bodies within the body of the insect from where it does no harm.
Why would insect use "excretion by storage"?
2. Insects do not drink!
How do they (insects) get their water?
They get all the water they need from the food they eat and from the chemical breakdown of carbohydrate in which water is a by-product.
3. Reasons why insects are very successful group of animals: they can conserve water, hence, they are found everywhere even in the hottest and driest places on earth.
What are those factors enabling insects to conserve water?
Presence of wax on the outer layer which makes their outer surface waterproof;
Presence of spiracles to prevent water loss from the gaseous exchange surface which is inside the body;
Possession of efficient excretory system.

MAMMALS
The excretory system of a mammal consists of:
the kidneys;
the ureters;
the bladder;
the urethra.













                                                                      Excretory system of man
The longitudinal section of mammalian kidney


Structure of the kidney

A kidney is a reddish organ. It is bean-shaped with fibrous capsule. It is located at the dorsal wall of the abdomen. It is made up of three regions; the cortex (outer region), the medulla (inner region) and the pelvis (the funnel-shaped space). It is highly vascularised with many capillaries which are all branches of renal artery and renal vein. At the top/apex of each kidney lies the adrenal gland.

Structure of a urinary tubule

The kidney is made up of functional units, each is called a kidney tubule or nephron. A human kidney contains over one million nephrons. At the anterior end, each nephron is made up of cup-shaped and hollow structure called bowman's capsule, and a long tube called convoluted tubule. In the hollow of the bowman's capsule, there is a mass of blood capillaries called glomerulus. These blood capillaries in the glomerulus are branches of the renal artery, which brings blood from the dorsal aorta to the kidney. The glomerulus and the bowman's capsule form the malpighian body/corpuscle.
The capsule (i.e. Bowman's capsule) opens into a short coiled tube, the proximal convoluted tubule, which lies in the cortex and joins the bowman's capsule anteriorly and the loop of Henle posteriorly. Then the tubule goes back, as the ascending tubule, from the medulla to the cortex region, where it is again coiled and is known as the distal convoluted tubule. The distal convoluted tubule joins a collecting tubule, which passes through the medulla region and opens at the pelvis.

The capillaries in the glomerulus rejoin to form a blood vessel leading out of the capsule. This vessel then branches into a capillary network around the urinary tubule before rejoining to form a branch of the renal vein. Through the renal vein, blood from the kidney flows to the posterior vena cava and thence back to the heart.

Note: the proximal convoluted (coiled) tubule forms the Henle loop in the medulla when it descends and form a U-shaped structure.


The kidney nephron

Mechanism of kidney excretion in mammals or how the kidney carries out its function of urine formation and discharge

The processes of urine formation include:
Ultrafiltration;
Selective reabsorption;
Tubular secretion
Blood from the heart flows to the glomerulus under high pressure, resulting in filtration of amino acids, glucose, mineral salts, water and urea out of the thin walled capillaries into the the Bowman's capsule. This process of filtering materials from the glomerulus into the Bowman's capsule is called ultra filtration or pressure filtration.

Note: the liquid that filters from the blood into the space inside the Bowman's capsule is called the glomerular filtrate. It is similar to blood plasma, but does not contain blood corpuscles or blood proteins.

The fluid that filters into the Bowman's capsule flows down the tubule, therefore bringing about selective reabsorption of useful substances back into the blood in the blood capillaries. Hence, at the proximal convoluted tubule, those useful substances such as glucose, amino acids, mineral salts and water are reabsorbed into the blood capillaries against concentration gradient or by active transport.
All the urea, small amounts of mineral salts and water are left in the tubule.

The fluid in the tubule becomes more concentrated as it flows through the distal tubule where more water is reabsorbed by the action of anti-diuretic hormone (ADH) and urine is finally formed.

Note: During ultrafiltration, bigger molecules like plasma proteins and the blood cells cannot pass through the wall of capillaries, hence, they are returned back into the blood.

Note: The filtered blood leaving the kidney by the renal vein contains:
less oxygen and glucose, and more carbon dioxide, as a result of cellular respiration; and
less nitrogenous wastes, salts and water as a result of excretion.

Reasons why blood flowing from the heart to the glomerulus is under high pressure.
The blood capillaries in the glomerulus have narrow diameter relative to the renal artery.
The blood capillaries that leave the glomerulus, are narrower in diameter than those that lead into it.
A large amount of blood flows through the kidney.
Note: It is estimated that about one quarter of the blood that leaves the heart with each beat flows through the kidney. When a large volume of blood flows through narrow capillaries, which offer a resistance to the flow of blood, a high pressure is built up.

How urine formed is expelled:
Urine passes through the ureter to the bladder where it is stored. The bladder has a muscle at its posterior end called a sphincter, which closes the outlet of the bladder. When one is ready to urinate; when the bladder is full, it contracts, while the sphincter relaxes and hence, the urine is discharged/expelled through the urethra.



Other functions of the kidney:
Osmoregulation
Maintenance of acid-base balance of the blood
Note: urinary tubule/kidney nephron is the functional unit of the kidney.

Class work
1. Relate the environment of three types of vertebrates of your choice to their;
type of excretory wastes, and
means of excretion.
2. Assess the reason why blood is not found in the urine, whereas mineral salts are present in it.
3. Suggest three factors that dictate the forms of nitrogenous waste excreted by an animal.
4. Compare excretion in insects and amphibians with respect to the:
structure of their organs of excretion;
mechanisms of excretion, and
forms of excreted wastes.
5. The liver cells make bile, which  is needed for the digestion of fats. Justify with explanatory reason(s) why the bile salt is considered excretory product.
6. Describe the process of excretion through the mammalian skin.
7. How would you explain the pungent odor of the expelled urine in man?


Excretion in Plants

Plants do not have special excretory organs. Gaseous wastes diffuse through the stomata, while insoluble excretory products are stored in some of the cells. Such non-gaseous wastes are excreted in the form of insoluble oil droplets, crystals and granules. The main excretory organs of flowering plants are the stomata in the leaves and lenticels in the stem. The main excretory products formed in plants are water, carbon dioxide and oxygen.
Mechanism of Excretion in Plants
Plants have their waste products eliminated through:
Transpiration;
Respiration;
Photosynthesis;
Guttation.
Note: These processes require diffusion.

Through transpiration, photosynthesis and respiration, excess water is lost in form of vapor i.e. through respiration and transpiration; likewise carbon dioxide i.e. respiration; oxygen i.e. photosynthesis and as droplets (e.g. In tomato, potato, grass) of water i.e. guttation. Other insoluble materials such as tannins, mucilage, gum, crystals, alkaloids and anthocyanin are stored in the bark of stems, leaves and petals, which are shed periodically.
Note: wastes stored in the bark of stem, leaves and petals can be removed from plants by the process of leaf-fall.

Assignment
Provide the economic importance of the following insoluble wastes in plants:
Tannins;
Gums;
Alkaloids

CELL REACTIONS TO ITS ENVIRONMENT
Responses
There are three types of responses. These are tactic, nastic, and  tropic movements.
The ability of a living organism to respond to stimulus is called irritability. A stimulus is an environmental change which induces or brings about a response in a cell or organism.

Taxis or Tactic Movements
Taxis is the directional movement of a whole organism or a free moving part of it, towards or away from a stimulus. This type of response is positive if the organism moves towards the stimulus, and negative if it moves away from it.
Examples of tactic responses:

Nastism or Nastic Movements
Nastism is a non-directional movement(response) of part of a plant to a non-directional stimuli.
Examples of nastic movements are:
closing of the morning glory flower when the light intensity is low;
the petals of sunflower which open in the light and close in the dark;
the folding of the leaflets of the Mimiosa plant when it is touched;
the closing of the leaflets of the flamboyant tree i.e. sleeping movements due to low light intensity.

Tropism or Tropic Movements
This is a directional movement of part of a plant to a directional stimuli; either towards or away the stimuli.  It is a very slow growth movements. It is a bending growth movement, by a plant organ, in response to a stimulus from one direction, by which the plant organ assumes from one direction, by which the plant organ assumes a particular posture or orientation, which bears a relationship to the direction from which the stimulus is received. This type of response is positive if the plant organ moves towards the stimulus, and negative if it moves away from it.
Examples of tropic response:

Class work
In a tabular form, give five differences between;
tropic movement and nastic movement;
tactic movement and tropic movement;
tactic movement and nastic movement.
2. Mention five organs of higher plants that respond to stimuli.

Experiment 1
Aim: To show that shoots are positively phototropic.
Materials required: two boxes, seedlings growing in pot, knife, aluminium foil.
Procedure: The two boxes are arranged as seen in the diagrams below. Some germinating bean seeds/or maize seeds are placed in two boxes with a hole cut at one end. Box A contains normal seedlings while box B contains seedlings with caps of aluminium foil over the tips of the shoots. The inside of each box is painted black to prevent light reflection. The entire experiment is put on the window and observed for a few days.



Observation: The shoot of the seedlings in box A will be observed to bend towards the source of light while those in box B grow straight.
Conclusion: Since the shoot of seedlings bend towards light, it shows that the shoot is positively phototropic.

Experiment 2
Aim: To show that the roots of plants are positively hydrotropic.
Materials required: Two large beakers, water, maize/beans seedlings.
Procedure: Two large beakers in which some bean seedlings are growing by the sides are used. Small holes are made at the center of the two beakers as shown below. A little water is poured at the center in one of the beakers (i.e. control experiment) while there is no water in the second beaker. The entire set-up is allowed to remain for few days.
A B
Observation: At the end of the experiment, the seedlings from both beakers are removed. The seedlings in which the beaker contains water bend their roots towards the source of water while the roots of the other beaker with no water remain straight.
Conclusion: The bending of the roots towards the source of water shows that the roots are positively hydrotropic.
Movement
Movement is the ability of living organisms to change position in response to stimulus (internal or external). It brings about a change of shape, form or position; effects of movement.
Protoplasmic streaming or cyclosis.
Cyclosis is the circulation of protoplasm in cells.
Importance of cyclosis: brings about circulation of materials within the cell. This results in bringing cell to life.
Causes of cyclosis.
Cyclosis is brought about by two actions. They are:
Ability of cytoplasm to change from plasma gel to plasma soil, progressively, from the anterior end to the posterior end of the stream;
Exertion of pressure at the posterior end of plasmasol by the cytoplasm causing the cell to move forward.
Examples of cyclosis.
Amoeboid movement by Amoeba and white blood cell.
Reproduction
Reproduction is the ability of living organisms to give rise to new individuals of the same species.
Forms or types of reproduction.
There are two main types of reproduction. These are asexual and sexual reproduction.
Asexual reproduction does not involve fusion of gametes, while sexual reproduction involves the fusion of sex cells or gametes.
Differences between Asexual and Sexual Reproduction

Asexual Reproduction.
It is common among simple organisms, as well as, flowering plants. It can be divided into two, namely:
Natural asexual reproduction;
Vegetative reproduction.
Note: In organisms which can reproduce both sexually and asexually, asexual reproduction occurs when food is plentiful and environmental conditions are favorable for growth.
Types of natural asexual reproduction in plants and animals:


Binary fission in Amoeba Budding in yeast





Spore formation in Rhizopus





Types of Vegetative Reproduction
There are two types of vegetative reproduction. These are:
Natural vegetative reproduction; and
Artificial vegetative reproduction.
Natural vegetative reproduction: This method involves the production of new individuals from the vegetative parts of the plants. Such vegetative parts include stems, roots and leaves.
Forms of natural vegetative reproduction are:
I.Use of modified underground stem:




II. Use of fleshy leaves to produce buds:







Bryophyllum leaf.                         Corm of Cocoyam.                            An onion bulb.
2. Artificial vegetative reproduction: This involves the use of intelligence by man to grow new plants from cut portion of the vegetative body of an older parent plants.



Cassava stem cutting Layering in cocoa Budding using Lemon (as a stock) and orange (as a scion)



Grafting using lemon (as a stock) and orange (as a scion)





Marcotting (stages a, b, c and d)in Mango
Importance of budding and grafting
They are used to propagate many fruit trees, especially citrus trees
Such trees propagated by budding and grafting bear fruits quickly
The trees possess resistance to diseases and other environmental resistance.
Advantages of vegetative propagation
Growth in young plant is rapid since there is no resting period.
Plants that do not produce seeds can only be propagated vegetatively.
Offspring are identical to the parent.
Young plant uses food reserves of the parent as it becomes easily established.
Only one parent is needed.
Desirable characters are retained.
Offspring mature more rapidly.
Plants are less susceptible to adverse weather condition.
It is independent of agents of pollination.
While becoming established, plants grown vegetatively require less care than seedlings.
Disadvantages of vegetative propagation
It may lead to overcrowding of plants.
No new variety of species are produced.
Disease of parents can easily be transmitted to offspring.
There is no mixing of characters.
It reduces resistance to disease.
Undesirable characters are easily transmitted to offspring.
It brings about competition among offspring and parents.
It reduces resistance to changes in climate.
Colonization of new localities is unlikely since offspring are always produced close to parent plant.


Sexual Reproduction.
In sexual reproduction, offsprings are produced by fusion of two different sex cells (gametes) which usually come from two different parents. When the two gametes come together, their nuclei fuse, and this is called fertilization. This fusion results in the formation of zygote, which later develops into an embryo.
Types of sexual reproduction
There are two major types of sexual reproduction. These are:
conjugation,
fusion of gametes.
Conjugation: This is the process by which nuclear material is passed from one cell to another. That is, the whole cell act as a gamete, and pair with another similar whole cell and exchange nuclei. It is common among lower organisms. Examples include Mucor, Rhizopus, Paramecium and Spirogyra.
Fusion of gametes: This is the union of the haploid male and female gametes to produce diploid organisms called zygote. The male gamete is the sperm in animal and the pollen grains in flowering plants, while the female gamete is the egg or ovum in animal and the ovule or egg in flowering plants. Examples of organisms using this methods include Moss, Ferns, all flowering plants, Hydra, Earthworm, Insects, and all vertebrates.
Advantages of sexual reproduction.
It enhances speciation or formation of new species or formation of new species and allows for the continuity of the species.
It provides the means for the maintenance of chromosome number from generation to generation.
It permits variability of individuals, i.e. new varieties are produced.
It enhances survival in new or changing environment.
It allows for the production of hybrids for some desirable traits.

EXCRETION
Excretion is the removal of waste metabolites from the body of a living organism. Examples of excretory products are sweat, urea, urine, carbon dioxide, oxygen (in plants), water (in plants), and uric acid.
TYPES OF EXCRETORY SYSTEM

GROWTH
Growth is an irreversible increase in size and or dry mass. Cell division by mitosis, cell enlargement and differentiation form the basis for growth.
Aspects of Growth
Increase in number of cells
Increase in number and size (height, length, breath, girth)
Increase in dry mass
Differentiation of cells into tissues and organs
Synthesis of new body material.
Process of Growth
Assimilation
Expansion of the cell
Cell division
Differences between Plants and Animals Growth

Similarities between growth in plants and animals
Both multicellular plants and animals grow by mitotic cell division of pre-existing cells to form new cells
Both achieve a certain amount of vegetative or body growth before reproductive growth sets in
Both show sigmoid growth curve in which the rate of growth is slow at first, becomes faster later until the maximum is reached, then growth rate starts to decline
Both plants and animals require food for growth
Both secrete growth hormones for growth
Growth is irreversible in both plants and animals.
Types of Cell Division
 Mitosis: This is a process of cell or nuclear division during which each chromosome in the nucleus duplicates itself and two new cells are formed with equal number of chromosomes i.e. the division of a somatic cell into two daughter cells. It takes place in the somatic cells i.e. body cells that are not involved in the production of gametes.
Mitosis consists of a division of the nucleus followed by a division of the cytoplasm.
Stages of Mitosis
Interphase: during this stage, cell is not dividing; no chromosomes is visible
Prophase: there are two prophase stages: (a) early prophase and (b) late prophase.
Early prophase:  during this stage, centriole pairs separate and move to opposite poles; aster rays form around centriole pairs; spindle fibres develop between the centriole pairs to form a spindle; chromosomes become visible in nucleus, then shorten and thicken. Each chromosome can be seen to be made up of two chromatids joined at the centromere.
Late prophase: during this stage, nuclear membrane disappears, and the chromosomes lie free in the cytoplasm.
Metaphase: during this stage, chromosomes come to lie around the equator of the cell.
Anaphase: during this stage, the two chromatids in each chromosome separate at the centromere, and are moved towards opposite poles, along the spindle fibres.
Telophase: this is the last stage of mitosis, during which chromatids arrive at the poles, spindle gradually disappears. A nuclear membrane forms around each set of chromatids. Chromatids gradually become invisible.
This is the end of nuclear division proper. It is followed by the division of the cytoplasm.
Importance or Role of Mitosis
It promotes cell growth
It helps in the replacement or repair of damaged tissues
It serves as basis of asexual or vegetative reproduction
It produces genetically or identical offspring which are identical to the parents
It maintains the diploid number of the chromosome of the cell
Life examples of mitotic process in animals
Formation of new cells in the malpighian layer of the skin
Production of red blood and white blood cells in the bone marrow
Cell division in the liver
Binary fission e.g. in Amoeba
Repair or healing of wound
Life examples of mitotic process in plants
Mitosis occurs in root tip or apex
It occurs in stem tip or apex
It occurs in cambium
It is found in meristems
(b) Meiosis:  A kind of cell division during spermatogenesis (sperm formation) and oogenesis (egg formation) in which there is a reduction of chromosomes to half of the original number of chromosomes.
Note: during gametogenesis (sperm and egg formation), in humans, the 46 chromosomes are reduced to 23. Therefore, each sperm or egg now has 23 chromosomes. The fusion of the sperm and egg gives 46 chromosomes which every human being has.
Importance or Roles of Meiosis
It results in the formation of sperms in animals
It results in the formation of eggs in animals
It results in the formation of pollen grains in anthers of flowering plants
It results in the formation of ovules in ovary of flowering plants.
Life examples or areas where meiosis occurs in plants
Ovaries
Anthers
Life examples or areas where meiosis occurs in animals
Ovaries
Testes
Differences between Mitosis and Meiosis

Similarities between mitosis and meiosis
Both result in the formation of new daughter cells
Both involves division of nucleus preceding division of cytoplasm
Both require hormones
Both take place in plants and animals cells
Both pass through prophase, metaphase, anaphase, and telophase.
Regions of Fastest Growth in Plants
The regions of fastest growth in plants are the roots and stem apices i.e. apical meristems. The apical meristems consist of meristematic cells i.e. cells capable of active division.
Note: the stem apices include the terminal buds and the lateral axillary buds.
Roles of apical meristems
Bring about growth in length (height) of the plant
Give rise to branches, leaves and flower in the shoot
They bring about primary growth (i.e. the first growth) of a plant.
Factors Affecting Growth in Plants
External factors:
Warm temperature
Adequate sunlight
Adequate water/humidity
Mineral salts/nutrients availability
Sufficient oxygen/air
Adequate carbon dioxide
pH level
accumulation of metabolic products
Internal factors:
Hormones i.e. the growth hormones e.g. auxins, gibberellings and cytokinins
Genetic constitution
   Factors Affecting Growth in Animals
Balanced diet
Oxygen/air
Warmth/suitable temperature
Heredity/genetic constitutions
Hormones
Growth curves
There is a pattern to which, by and large, is shared by both plants and animals.
Growth pattern in plants: in annual plants, a typical sigmoid growth curve is exhibited with limited growth, while in perennial plants; a series of sigmoid curve is exhibited with unlimited growth.

Growth pattern in animals: in most invertebrates, such as fishes, they show  S-shaped or sigmoid curve with unlimited growth. In arthropods, such as insects, they moult time to time, hence this growth is called intermittent growth and the growth curve is sigmoid. In birds and mammals e.g. human they show limited growth with sigmoid curve.

NUTRITION/FEEDING
Nutrition: This is the process by which living organisms obtain and utilize food materials from external environment in order to supply the nutrients required for metabolic activities.
Food: This is any substance which when absorbed into the body cells yields energy and materials for growth, repairs of damaged tissues and regulation of body processes without harming the living organism. Food is the source of nutrients.


Usefulness of food
Living cells or organisms require food for the following reasons:
To provide energy needed for various life activities;
To make essential substances such as hormones and enzymes;
To make new cells for growth and replacement of worn-out tissues;
To supply various substances required for healthy growth and development
Modes/Types of Nutrition
The following are the types of nutrition:
Autotrophic nutrition (self-feeders); and
Heterotrophic nutrition (dependent-feeders)
Autotrophic nutrition: A type of nutrition in which organisms are able to manufacture their own organic food (i.e. glucose) from simple carbon compound and simple inorganic nitrogen . Such organism is referred to as autotroph,
Types of autotrophic nutrition
Photosynthetic (holophytic) e.g. green plants;
Chemosynthetic nutrition i.e. some bacteria e.g. blue-green algae; nostoc, suphur bacteria, Nitrosomonas e.t.c.
      2.    Heterotrophic nutrition: A type of nutrition carried out by organisms that are not capable of manufacturing their own food from simple inorganic substances. Such organism is called heterotroph
Types of heterotrophic nutrition
Holozoic nutrition: This is a type of nutrition in which food is obtained as a solid organic material, eaten, digested and absorbed into the body. Nearly all animals are holozoic in nutrition.
Saprophytic nutrition: This is a type of nutrition in which non-green plants feed on dead and decaying organic matter.
Note: organisms which feed saprophytically are known as saprophytes. Examples are most fungi (e.g. Mucor, Mushroom, and Yeast) and bacteria.
Symbiotic nutrition: This is a type of nutrition in which two organisms of different species live together to take advantage of each other. Examples are the association between alga and a fungus to form lichens, where the fungus provides moisture (i.e. water), mineral salts and support for the alga which the alga used in manufacturing food by photosynthesis for the fungus and itself; other example is the relationship between herbivorous animals (e.g. goat, sheep) and cellulose-digesting bacteria that live in the caecum and colon of herbivores.
Parasitic nutrition: This is a type of nutrition in which one organism obtains food from another organism and during the feeding process one organism is harmed and does not benefit. The organism causing harm is called parasite, while the one been harmed is called host.
Note: the association between a host and a parasite is called parasitism. Examples of parasites are Plasmodium, Ascaris lumbricoides, ticks, bugs e.t.c.




ROLES OF ENZYMES IN DIGESTION
Enzymes are organic catalysts of protein origin produced by living cells which help to speed up or slow down the rate of chemical reactions but remain unchanged chemically at the end of the reaction.
We shall discuss this in detail next term!

MINERAL SALTS
Mineral salts are contained in important elements. They have to be taken in compound forms, for example sodium chloride (table salt) is a compound of sodium and chlorine.
Why do we have to take mineral elements in compound forms?
Because if they are taken like that i.e. as mineral elements, they could be fatal but when taken in a compound form, they become harmless and useful to the body.
The soil is the main source of mineral salts, while gaseous elements such as oxygen, hydrogen and carbon are mainly derived from the atmosphere.
Classes of elements or plant nutrients
Plant nutrients are grouped into two classes depending on the quantity that is required by plants. The classes are:
Macro-nutrient or major elements: They are required by plants in large quantities for healthy growth and development. Examples are nitrogen, phosphorus, potassium, magnesium, calcium, oxygen, hydrogen, carbon, sulphur and iron.
Micro-nutrients or trace elements: They are required by plants in small quantities for healthy growth and development. Examples are zinc, copper, boron, molybdenum, cobalt, chlorine, and manganese, fluorine and iodine.
METABOLISM
Metabolism is the physical and chemical processes by which simple molecules of food are built up into complex molecules (assimilation, anabolism)and complex molecules are broken down into simple molecules (respiration)with liberation of energy for work by the organism.
Types of metabolism
Anabolism: This is the building up of simple molecules of food into complex molecules by living things, with the use of energy leading to an increase in size and complexity. Anabolism, or constructive metabolism, is the process of synthesis required for the growth of new cells and the maintenance of all tissues.
 Examples of anabolic processes are:
formation of glycogen from glucose;
formation of starch from glucose;
formation of proteins from amino acids;
formation of fats and oil from fatty acids and glycerol;
photosynthesis in green plants
growth
Catabolism: This is the breakdown of complex food molecules by living things with liberation of energy for work. It is the production of energy through the conversion of complex molecules into simple ones. Catabolism, or destructive metabolism, is a continuous process concerned with the production of the energy required for all external and internal physical activity.
Examples of catabolic processes are:
Respiration;
Fermentation;
Digestion.
Note:
When anabolism exceeds catabolism, growth or weight gain occurs. When catabolism exceeds anabolism, such as during periods of starvation or disease, weight loss occurs. When the two metabolic processes are balanced, the organism is said to be in a state of dynamic equilibrium.

Usefulness of energy released during metabolism
Energy released during metabolic activities is the ATP, which is used for the following purposes:
Anabolic process: ATP provides the energy necessary to build up macro molecules, e.g. proteins from amino acids;
Active transport: Energy is needed to move materials against a concentration gradient, e.g. by the use of ion pumps;
Movement: Muscle contraction, ciliary movement and contraction of the spindle fibers during cell division all require energy from the hydrolysis of ATP;
Activating reactants: Chemicals often require the addition of phosphate groups from ATP to make them more reactive, e.g. phosphorylation of glucose at the beginning of glycolysis;
Secretion: ATP provides energy for the secretion of cell products.
Uses of glucose
Builds new plant materials;
Used by plant as energy source;
Eaten by animal and used as energy source;
Used in building new animal materials.
Uses of ATP (adenosine triphosphate)
For chemical work (e.g. enzyme synthesis)
For mechanical work (e.g. muscle contraction)
For osmotic work e.g. water regulation
For electrical work e.g. nerve impulse transmission
For cell division i.e. it provides energy required by cells to divide

CELLULAR/INTERNAL/TISSUE RESPIRATION
This is the process of breaking down glucose by a series of chemical reactions controlled by enzymes to release energy. It may also be defined as the oxidation of food substance in the cells (particularly in the mitochondria), to release energy for work. The energy released is stored in adenosine triphosphate (ATP).
Differences between glucose and ATP


Types of cellular respiration
Aerobic respiration: it requires oxygen to break down/oxidize glucose/simple sugar (substrates) in the cell to release carbon (IV) oxide and water.i.e.
C6H12O6 + 6O2 →6CO2 + 6H2O + 38ATP
Anaerobic respiration: it does not require oxygen to break down glucose in the cells to release alcohol, carbon dioxide and 2 ATP as the products. i.e.
C6H12O6 → C2H5OH + 2CO2 + 2ATP
Chemical processes of cellular respiration
The breaking down of glucose in the body passes through several pathways before it can produce energy. These pathways are Glycolysis and Kreb’s cycle
Glycolysis: This is a series of chemical reactions which involves the breaking down of glucose to a 3-carbon molecule called pyruvic acid.
Note: what happens to the pyruvic acid depends on the presence or absence of oxygen. For example in animals, the pyruvic acid is converted to lactic acid. But in plant, the pyruvic acid is converted to alcohol; this is known as alcoholic fermentation.
Examples of organism that undergoes fermentation is yeast
Kreb’s cycle/citric acid cycle/tricarboxylic acid(TAC): This is a series of cyclic reactions which begin with the pyruvic acid formed from glycolysis which combined with acetyl co-enzyme A to form citric acid.
Differences between Glycolysis and Kreb’s cycle

Similarities between aerobic and anaerobic respiration
Both lead to the release of energy
Both occur in plant and animal cells
Both require enzymes to speed up the reactions
Both lead to generation of heat
Both give off carbon dioxide as by-product.
Differences between aerobic and anaerobic respiration


E

NUTRITION/FEEDING
Nutrition: This is the process by which living organisms obtain and utilize food materials from external environment in order to supply the nutrients required for metabolic activities.
Food: This is any substance which when absorbed into the body cells yields energy and materials for growth, repairs of damaged tissues and regulation of body processes without harming the living organism. Food is the source of nutrients.


Usefulness of food
Living cells or organisms require food for the following reasons:
To provide energy needed for various life activities;
To make essential substances such as hormones and enzymes;
To make new cells for growth and replacement of worn-out tissues;
To supply various substances required for healthy growth and development
Modes/Types of Nutrition
The following are the types of nutrition:
Autotrophic nutrition (self-feeders); and
Heterotrophic nutrition (dependent-feeders)
Autotrophic nutrition: A type of nutrition in which organisms are able to manufacture their own organic food (i.e. glucose) from simple carbon compound and simple inorganic nitrogen . Such organism is referred to as autotroph,
Types of autotrophic nutrition
Photosynthetic (holophytic) e.g. green plants;
Chemosynthetic nutrition i.e. some bacteria e.g. blue-green algae; nostoc, suphur bacteria, Nitrosomonas e.t.c.
      2.    Heterotrophic nutrition: A type of nutrition carried out by organisms that are not capable of manufacturing their own food from simple inorganic substances. Such organism is called heterotroph
Types of heterotrophic nutrition
Holozoic nutrition: This is a type of nutrition in which food is obtained as a solid organic material, eaten, digested and absorbed into the body. Nearly all animals are holozoic in nutrition.
Saprophytic nutrition: This is a type of nutrition in which non-green plants feed on dead and decaying organic matter.
Note: organisms which feed saprophytically are known as saprophytes. Examples are most fungi (e.g. Mucor, Mushroom, and Yeast) and bacteria.
Symbiotic nutrition: This is a type of nutrition in which two organisms of different species live together to take advantage of each other. Examples are the association between alga and a fungus to form lichens, where the fungus provides moisture (i.e. water), mineral salts and support for the alga which the alga used in manufacturing food by photosynthesis for the fungus and itself; other example is the relationship between herbivorous animals (e.g. goat, sheep) and cellulose-digesting bacteria that live in the caecum and colon of herbivores.
Parasitic nutrition: This is a type of nutrition in which one organism obtains food from another organism and during the feeding process one organism is harmed and does not benefit. The organism causing harm is called parasite, while the one been harmed is called host.
Note: the association between a host and a parasite is called parasitism. Examples of parasites are Plasmodium, Ascaris lumbricoides, ticks, bugs e.t.c.




ROLES OF ENZYMES IN DIGESTION
Enzymes are organic catalysts of protein origin produced by living cells which help to speed up or slow down the rate of chemical reactions but remain unchanged chemically at the end of the reaction.
We shall discuss this in detail next term!

MINERAL SALTS
Mineral salts are contained in important elements. They have to be taken in compound forms, for example sodium chloride (table salt) is a compound of sodium and chlorine.
Why do we have to take mineral elements in compound forms?
Because if they are taken like that i.e. as mineral elements, they could be fatal but when taken in a compound form, they become harmless and useful to the body.
The soil is the main source of mineral salts, while gaseous elements such as oxygen, hydrogen and carbon are mainly derived from the atmosphere.
Classes of elements or plant nutrients
Plant nutrients are grouped into two classes depending on the quantity that is required by plants. The classes are:
Macro-nutrient or major elements: They are required by plants in large quantities for healthy growth and development. Examples are nitrogen, phosphorus, potassium, magnesium, calcium, oxygen, hydrogen, carbon, sulphur and iron.
Micro-nutrients or trace elements: They are required by plants in small quantities for healthy growth and development. Examples are zinc, copper, boron, molybdenum, cobalt, chlorine, and manganese, fluorine and iodine.
METABOLISM
Metabolism is the physical and chemical processes by which simple molecules of food are built up into complex molecules (assimilation, anabolism)and complex molecules are broken down into simple molecules (respiration)with liberation of energy for work by the organism.
Types of metabolism
Anabolism: This is the building up of simple molecules of food into complex molecules by living things, with the use of energy leading to an increase in size and complexity. Anabolism, or constructive metabolism, is the process of synthesis required for the growth of new cells and the maintenance of all tissues.
 Examples of anabolic processes are:
formation of glycogen from glucose;
formation of starch from glucose;
formation of proteins from amino acids;
formation of fats and oil from fatty acids and glycerol;
photosynthesis in green plants
growth
Catabolism: This is the breakdown of complex food molecules by living things with liberation of energy for work. It is the production of energy through the conversion of complex molecules into simple ones. Catabolism, or destructive metabolism, is a continuous process concerned with the production of the energy required for all external and internal physical activity.
Examples of catabolic processes are:
Respiration;
Fermentation;
Digestion.
Note:
When anabolism exceeds catabolism, growth or weight gain occurs. When catabolism exceeds anabolism, such as during periods of starvation or disease, weight loss occurs. When the two metabolic processes are balanced, the organism is said to be in a state of dynamic equilibrium.

Usefulness of energy released during metabolism
Energy released during metabolic activities is the ATP, which is used for the following purposes:
Anabolic process: ATP provides the energy necessary to build up macro molecules, e.g. proteins from amino acids;
Active transport: Energy is needed to move materials against a concentration gradient, e.g. by the use of ion pumps;
Movement: Muscle contraction, ciliary movement and contraction of the spindle fibers during cell division all require energy from the hydrolysis of ATP;
Activating reactants: Chemicals often require the addition of phosphate groups from ATP to make them more reactive, e.g. phosphorylation of glucose at the beginning of glycolysis;
Secretion: ATP provides energy for the secretion of cell products.
Uses of glucose
Builds new plant materials;
Used by plant as energy source;
Eaten by animal and used as energy source;
Used in building new animal materials.
Uses of ATP (adenosine triphosphate)
For chemical work (e.g. enzyme synthesis)
For mechanical work (e.g. muscle contraction)
For osmotic work e.g. water regulation
For electrical work e.g. nerve impulse transmission
For cell division i.e. it provides energy required by cells to divide

CELLULAR/INTERNAL/TISSUE RESPIRATION
This is the process of breaking down glucose by a series of chemical reactions controlled by enzymes to release energy. It may also be defined as the oxidation of food substance in the cells (particularly in the mitochondria), to release energy for work. The energy released is stored in adenosine triphosphate (ATP).
Differences between glucose and ATP


Types of cellular respiration
Aerobic respiration: it requires oxygen to break down/oxidize glucose/simple sugar (substrates) in the cell to release carbon (IV) oxide and water.i.e.
C6H12O6 + 6O2 →6CO2 + 6H2O + 38ATP
Anaerobic respiration: it does not require oxygen to break down glucose in the cells to release alcohol, carbon dioxide and 2 ATP as the products. i.e.
C6H12O6 → C2H5OH + 2CO2 + 2ATP
Chemical processes of cellular respiration
The breaking down of glucose in the body passes through several pathways before it can produce energy. These pathways are Glycolysis and Kreb’s cycle
Glycolysis: This is a series of chemical reactions which involves the breaking down of glucose to a 3-carbon molecule called pyruvic acid.
Note: what happens to the pyruvic acid depends on the presence or absence of oxygen. For example in animals, the pyruvic acid is converted to lactic acid. But in plant, the pyruvic acid is converted to alcohol; this is known as alcoholic fermentation.
Examples of organism that undergoes fermentation is yeast
Kreb’s cycle/citric acid cycle/tricarboxylic acid(TAC): This is a series of cyclic reactions which begin with the pyruvic acid formed from glycolysis which combined with acetyl co-enzyme A to form citric acid.
Differences between Glycolysis and Kreb’s cycle

Similarities between aerobic and anaerobic respiration
Both lead to the release of energy
Both occur in plant and animal cells
Both require enzymes to speed up the reactions
Both lead to generation of heat
Both give off carbon dioxide as by-product.
Differences between aerobic and anaerobic respiration