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These are fats and oils.
Fats are solid at room temperature while oils are liquid.
They are made up of carbon, oxygen and hydrogen atoms.
The structural units of lipids are fatty acids and glycerol.
Fatty acids are made up of hydrocarbon chain molecules with a carboxyl group (-COOH) at one end.
In the synthesis of a lipid, three fatty acid molecules combine with one glycerol molecule to form a triglyceride.
Three molecules of water are lost in the process.
This is a condensation reaction and water is given off.
Lipids are hydrolysed e.g. during digestion to fatty acids and glycerol, water is added.
Condensation = Glycerol + 3 Fatty hydrolysis Lipid + Water acids 

Properties of Lipids

• Fats are insoluble in water but dissolve in organic solvents e.g. in alcohols.
• They are chemically inactive, hence used as food storage compounds.

Functions of Lipids

• Structural materials - as structural material they make up the cell membrane.
• Source of energy - they are energy rich molecules. One molecule of lipid provides more energy than a carbohydrate molecule.
• Storage compound - They are stored as food reserves in plants. In animals e.g. mammals, all excess food taken is converted to fats which are stored in adipose tissue, and around internal organs such as the heart and kidneys.
• Insulation - They provide insulation in animals living in cold climates. A lot of fat is stored under the skin e.g. blubber in seals.
• Protection - Complex lipids e.g. wax on leaf surfaces protects the plant against water-loss and overheating. Fats stored around some internal organs acts as shock absorbers, thus protecting the organs.
• Source of Metabolic Water -:-lipids when oxidised produce metabolic water which supplements water requirements in the body. Desert animals e.g. the camel accumulate large quantities of fat in the hump which when oxidised releases metabolic water.

Proteins

• Proteins are the most abundant organic compounds in cells and constitute 50% of total dry weight.
• Proteins are compounds which are made up of carbon, hydrogen, nitrogen, oxygen and sometimes sulphur and phosphorus.
• The structural units of proteins are amino acids.
• The nature of a protein is determined by the types of amino acids it is made of.
• There are about 20 common amino acids that make up proteins. 

Essential and Non-Essential Amino Acids

• Essential amino acids are those which cannot be synthesised in the body of an organism and must therefore be provided in the diet.
• There are ten amino acids which are essential for humans.
• These are valine, leucine, phenylalanine, lysine, tryptophan, isoleucine, methionine, threonine, histidine and arginine.
• Non-essential amino acids are those which the body can synthesise and therefore need not be available in the diet.
• There are ten of them.
• These are glycine, alanine, glutamic acid, aspartic acid, serine, tyrosine, proline, glutamine, arginine and cysteine.
• Proteins are essential in the diet because they are not stored in the body.
• Excess amino acids are deaminated.

Formation of Proteins

• Proteins are made up of many amino acid units joined together through peptide bonds.
• When two amino acids are joined together a dipeptide is formed.
• The chemical process involved is called condensation and a molecule of water is eliminated .
• When many amino acids are joined together a polypeptide chain is formed.
• The nature of a particular protein depends on the types, number and sequence of amino acids from which it is made. 

Functions of Proteins
As structural materials proteins-

• These are the basic building structures of protoplasms
• Proteins in conjunction with lipid form the cell membrane.

Examples of structural proteins include:

• Keratin (in hair, nails, hoofs, feathers and wool)
• Silk in spider's web.
• Elastin forms ligaments that join bones to each other.

Protective proteins.

• Antibodies that protect the body against foreign antigens.
• Fribrogen and thrombin are involved in clot formation, preventing entry of micro-organisms when blood vessel is cut.

 
As functional chemical compounds.
Examples are hormones and enzymes that act as regulators in the body.
Respiratory pigments.
Examples are haemoglobin that transports oxygen in the blood and myoglobin that stores up oxygen in muscles.
Contractile proteins - make up muscles, i.e. myosin and actin.
Proteins combine with other chemical groups to form important substances e.g. mucin in saliva.
Source of energy.
Proteins are a source of energy in extreme conditions when carbohydrates and fats are not available e.g. in starvation.

Enzymes

• Enzymes are biological catalysts that increase the rate of chemical reaction in the body.
• They are all produced inside cells.
• Some are intracellular and they catalyse reactions within the cells.
• Others are extracellular and are secreted out of the cells where they work. E.g. digestive enzymes.

Properties of Enzymes

• Enzymes are protein in nature.
• Enzymes are specific to the type of reaction they catalyse.
• This is referred to as substrate specificity.
• Enzymes work in very small amounts.
• They remain unchanged after the reaction.
• They catalyse reversible reactions.
• They work very fast (high turnover numbers) e.g. the enzyme catalase works on 600 thousand molecules of hydrogen peroxide in one second. 

Naming of enzymes
Enzymes are named by adding the suffix -ase to:
Name of substrate that they work on e.g.

• Carbohydrates - carbohydrases e.g.sucrase.
• Starch (amylose) - amylase
• Protein - proteinase (protease)
• Lipids -lipases

Type of chemical reaction catalysed e.g.

• Oxidation - oxidase
• Reduction - reductase
• Hydrolysis - hydrolase

Temperature

• Enzymes are sensitive to temperature changes.
• Generally, the rate of an enzyme-controlled reaction doubles with every 10OC increase in temperature.
• However, temperatures above 40°C do not favour enzyme reaction.
• This is because enzymes are denatured by high temperatures.

pH

• Every enzyme has a particular pH range over which it works best.
• Some enzymes work best in acidic media while others function better in alkaline media.
• Many enzymes function well under neutral conditions.

Enzyme Concentration

• Under conditions where the substrate is in excess, the rate of an enzyme-controlled reaction increases as the enzyme concentration is increased.

Substrate Concentration

• If the concentration of the substrate is increased while that of the enzyme remains constant, the rate of the reaction will increase for some time and then become constant.
• Any further increase in substrate concentration will not result in corresponding increase in the rate of the reaction.

Enzyme Inhibitors

• These are substances that either compete with substrates for enzyme active sites or combine with enzymes and hence they inhibit the enzyme reaction; e.g. certain drugs, cyanide and nerve gas.

Co-factors

• Most enzymes require the presence of other compounds known as co-factors which are non-proteins.
• There are three groups of co-factors.
• Inorganic ions - e.g. iron, magnesium, copper and zinc.
• Complex organic molecules known as prosthetic groups are attached to the enzyme e.g. flavin adenine dinucleotide (FAD) derived from vitamin B2 (riboflavin).
• Co-enzymes e.g. coenzyme A is involved in respiration.
• All co-enzymes are derived from vitamins.

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​TOPIC 5 - NUTRITION IN PLANTS AND ANIMALS [KCSE NOTES].pdf
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Meaning, importance and types of nutrition
Nutrition in plants (autotrophism)
Definition of photosynthesis and its importance in nature

1. Adaptations of leaf to photosynthesis
2. Structure and function of chloroplast
3. Process of photosynthesis - light and dark stages (omit details of electron transport system and chemical details of carbon dioxide fixation)
4. Factors influencing photosynthesis
   1. Light intensity
   2. Carbon dioxide concentration
   3. Water
   4. Temperature
   5. Chemical compounds which constitute living organisms
   6. Chemical composition and functions of carbohydrates, proteins and lipids (omit details of chemical structure of these compounds and mineral salts in plant nutrition).
5. Properties and functions of enzymes (omit lock and key hypothesis)
6. Nutrition in Animals (heterotrophism)
7. Meaning and types of heterotrophism
8. Modes of feeding in animals
9. Dentition of a named carnivorous, herbivorous and omnivorous mammal
10. Adaptation of the three types of dentition to feeding
11. Internal structure of mammalian teeth
12. Common dental diseases, their causes and treatment
13. Digestive system and digestion in a mammal (human)
14. Digestive system, regions, glands and organs associated with digestion
15. Ingestion, digestion, absorption, assimilation and egestion
16. Importance of vitamins, mineral salts, roughage and water in human nutrition
17. Factors determining energy requirements in humans

Practical activities

1. Carry out experiments on factors affecting photosynthesis
2. Observe stomata distribution
3. Carry out food test experiments
4. Carry out experiments on factors affecting enzymatic activities
5. Investigate presence of enzymes in living tissues (plants and animals)
6. Observe, identify, draw and label different types of mammalian teeth
7. Carry out dissection of a small mammal to observe digestive system and associated organs (demonstration)

By the end of the topic, the learner should be able to:

1. Define nutrition and state its importance in living organisms
2. Differentiate various modes of feeding
3. Describe photosynthesis and show its importance in nature
4. Explain how the leaf is adapted to photosynthesis
5. Explain the factors affecting photosynthesis
6. Distinguish between carbohydrates proteins and lipids
7. State the importance of various chemical compounds in plants and animals
8. Explain the properties and functions of enzymes
9. Relate various types of teeth in mammals to their feeding habits
10. Differentiate between omnivorous, carnivorous and herbivorous modes of feeding
11. Relate the structures of the mammalian (human) alimentary canal to their functions
12. Explain the role of enzymes in digestion in a mammal (human)
13. Explain the factors that determine energy requirements in humans.

​External Structure 
The external structure of the leaf consists of a leaf stalk or petiole and a broad leaf blade or lamina.
The lamina has a main vein midrib from which smaller veins originate.
The outline of the leaf is the margin and the tip forms the apex.

​Epidermis
This is the outer layer of cells, normally one cell thick.
It is found in both the upper and lower leaf surfaces.
The cells are arranged end to end.
The epidermis offers protection and maintains the shape of the leaf.
It is covered by a layer of cuticle which reduces evaporation.

Leaf Mesophyll
Consists of the palisade layer, next to upper epidermis, and the spongy layer next to the lower epidermis. 

Palisade Mesophyll Layer
The cells are elongated and arranged close to each other leaving narrow air spaces.
These contain numerous chloroplasts and are the main photosynthetic cells.
In most plants, the chloroplast are distributed fairly uniformly throughout the cytoplasm.
In certain plants growing in shaded habitats in dim light, most chloroplasts migrate to the upper region of the palisade cells in order to maximize absorption of the limited light available.

Spongy Mesophyll Layer
The cells are spherical in shape.
They are loosely arranged, with large intercellular spaces between them.
The spaces are air-filled and are linked to the stomatal pores.
The spongy mesophyll cells have fewer chloroplasts than the palisade mesophyll cells.

Vascular Bundles
These are made up of the xylem and the phloem tissues.
The xylem transports water and mineral salts to the leaves.
The phloem transports food manufactured in the leaf to the other parts of the plant and from storage organs to other parts.

Adaptations of Leaf for Photosynthesis
Presence of veins with vascular bundles.
Xylem vessels transport water for photosynthesis.
Phloem transports manufactured food from leaves to other parts of the plant.
Leaf lamina is thin to allow for penetration of light over short distance to reach photosynthetic cells.
Broad lamina provides a large surface area for absorption of light and carbon (IV) oxide.
Transparent cuticle and epidermal layer allow light to penetrate to mesophyll cells.
Palisade cells are close to the upper epidermis for maximum light absorption.
Presence of numerous chloroplasts in palisade mesophyll traps maximum light.
Chloroplast contain chlorophyll that traps light energy.
Spongy mesophyll layer has large intercellular air spaces allowing for gaseous exchange.
Presence of stomata for efficient gaseous exchange (entry of carbon (IV) oxide into leaf and exit of oxygen).
Mosaic arrangement of leaves to ensure no overlapping of leaves hence every leaf is exposed to light.

Structure and Function of Chloroplasts
Chloroplasts are large organelles (5 um in diameter) found in the cytoplasm of green plant cells.
They are visible under the light microscope.
They contain chlorophyll, a green pigment and other carotenoids which are yellow, orange and red in colour.
Certain plants have red or purple leaves due to abundance of these other pigments.
Chlorophyll absorbs light energy and transforms it into chemical energy.
The other pigments absorb light but only to pass it onto chlorophyll.

​The wall of chloroplast consists of an outer and an inner membrane.
The two make up the chloroplast envelop.
Inner membrane encloses a system of membranes called lamellae.
At intervals, the membranes form stacks of fluid filed sacs known as grana (singular granum).
Chloroplast and other pigments are attached to the grana.
In between the lamellae is a gel-like stroma that contains starch grains and lipid droplets.
Enzymes for the dark stage reaction (light independent stage) are embedded in the stroma.
Enzymes for the light dependent stage occur in the grana.

Functions of Chloroplast
Absorption of light by chlorophyll and other pigments.
Light stage of photosynthesis occurs on the grana. (Transformation of light energy to chemical energy.)
Carbon fixation to form carbohydrate takes place in the stroma which has enzymes for dark stage of photosynthesis.

​The reaction occurs in two main phases or stages.
The initial state requires light and it is called the light dependent stage or simply light stage.
It takes place on the lamellae surfaces.
Its products are used in the dark stage.
The dark stage does not require light although it occurs in the light and is called light independent stage.

Light-Stage
Two reactions take place that produce raw materials for the dark stage:
Light energy splits the water molecules into hydrogen and oxygen.
This process is called photolysis.
The hydrogen is taken up by a hydrogen acceptor called Nicotinamide adenine dinucleotide phosphate (NADP) while oxygen is released as a by-product.

​Light energy strikes the chlorophyll molecules and sets in motion a series of reactions resulting in the production of a high energy molecule called adenosine triphosphate (ATP).

​Dark Stage
This stage involves the fixation of carbon i.e. the reduction of carbon (IV) oxide by addition of hydrogen to form carbohydrate.
It uses the products formed during the light stage. Carbon (IV) oxide + Hydrogen = Carbohydrates
The synthesis of carbohydrates does not take place in a simple straight line reaction as shown in the equation above.
It involves a series of steps that constitute what is known as the Calvin cycle.
Carbon (IV) oxide is taken up by a compound described as a carbon (IV) oxide acceptor.
This is a 5-carbon compound known as ribulose biphosphate and a six carbon compound is formed which is unstable and splits into two three-carbon compounds.
Hydrogen from the light reaction is added to the three carbon compound using energy (ATP) from the light reaction.
The result is a three carbon (triose) sugar, (phosphoglycerate or PGA).
This is the first product of photosynthesis.
Glucose, other sugars as well as starch are made from condensation of the triose sugar molecules.
The first product is a 3-carbon sugar which condenses to form glucose (6-C sugar).
From glucose, sucrose and eventually starch is made.
Sucrose is the form in which carbohydrate is transported from the leaves to other parts of the plant. 
Starch is the storage product.
Other substances like oils and proteins are made from sugars.
This involves incorporation of other elements e.g. nitrogen, phosphorus and sulphur.

​Certain factors must be provided for before photosynthesis can take place.
The rate or amount of photosynthesis is also influenced by the quantity or quality of these same factors. 

Carbon (IV) Oxide Concentration
Carbon (IV) oxide is one of the raw materials for photosynthesis.
No starch is formed when leaves are enclosed in an atmosphere without carbon (IV) oxide.
The concentration of carbon (IV) oxide in the atmosphere remains fairly constant at about 0.03% by volume.
However, it is possible to vary the carbon (IV) oxide concentration under experimental conditions.
Increasing the carbon (IV) oxide concentration up to 0.1 % increases the rate of photosynthesis.
Further increase reduces the rate.

Light Intensity
Light supplies the energy for photosynthesis.
Plants kept in the dark do not form starch.
Generally, increase in light intensity up to a certain optimum, increases the rate of photosynthesis.
The optimum depends on the habitat of the plant.
Plants that grow in shady places have a lower optimum than those that grow in sunny places.
Water
Water is necessary as a raw material for photosynthesis.
The amount of water available greatly affects the rate of photosynthesis.
The more water available, the more the photosynthetic rate, hence amount of food made.
Effect of water on photosynthesis can only be inferred from the yield of crops.
It is the main determinant of yield (limiting factor in the tropics).
Temperature
The reactions involved in photosynthesis are catalysed by a series of enzymes.
A suitable temperature is therefore necessary.
The optimum temperature for photosynthesis in most plants is around 300C.
This depends on the natural habitat of the plant.
Some plants in temperate regions have 20°C as their optimum while others in the tropics have 45°C as their optimum temperature.
The rate of photosynthesis decreases with a decrease in temperature below the optimum.
In most plants, photosynthesis stops when temperatures approach O°C although some arctic plant species can photosynthesise at -2°C or even -3°C.
Likewise, increase in temperature above the optimum decreases the rate and finally the reactions stop at temperatures above 40°c due to enzyme denaturation.
However, certain algae that live in hot springs e.g. Oscilatoria can photosynthesis at 75°C
Chlorophyll
Chlorophyll traps or harnesses the energy from light.
Leaves without chlorophyll do not form starch.
Chemical Compounds Which Constitute Living Organisms
All matter is made up of chemical elements, each of which exists in the form of smaller units called atoms.
Some of the elements occur in large amounts in living things.
These include carbon, oxygen, hydrogen, nitrogen, sulphur and phosphorus.
Elements combine together to form compounds.
Some of these compounds are organic.
Organic compounds contain atoms of carbon combined with hydrogen and they are usually complex.
Other compounds are inorganic.
Most inorganic compounds do not contain carbon and hydrogen and they are usually less complex.
Cells contain hundreds of different classes of organic compounds.
However, there are four classes of organic compounds found in all cells.
These are: carbohydrates, lipids, proteins and nucleic acids.
Carbohydrates

• Carbohydrates are compounds of carbon, hydrogen and oxygen.
• Hydrogen and oxygen occur in the ratio of 2: 1 as in water.
• Carbohydrates are classified into three main groups: monosaccharides, disaccharides and polysaccharides.

Monosaccharides

• These are simple sugars.
• The carbon atoms in these sugars form a chain to which hydrogen and oxygen atoms are attached.
• Monosaccharides are classified according to the number of carbon atoms they possess.
• The most common monosaccharides are:
  • Glucose - found free in fruits and vegetables.
  • Fructose - found free in fruits and in bee honey.
  • Galactose - found combined in milk sugar.
• The general formula for these monosaccharides is (CH2O)n where n is 6.
• They have the same number of carbon, hydrogen and oxygen molecules i.e. C6H12O6.

Properties of Monosaccharides

• They are soluble in water.
• They are crystallisable.
• They are sweet.
• The are all reducing sugars.
• This is because they reduce blue copper (II) sulphate solution when heated to copper oxide which is red in colour and insoluble.

Functions of Monosaccharides

• They are oxidised in the cells to produce energy during respiration.
• Formation of important biological molecules e.g. deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
• Some monosaccharides are important metabolic intermediates e.g. in photosynthesis and in respiration.
• Monosaccharides are the units from which other more complex sugars are formed through condensation.

Disaccharides

• These contain two monosaccharide units.
• The chemical process through which a large molecule (e.g. a disaccharide) is formed from smaller molecules is called condensation and it involves loss of water.
• Common examples of disaccharides include sucrose, maltose and lactose.

​Disaccharides are broken into their monosaccharide units by heating with dilute hydrochloric acid.
This is known as hydrolysis and involves addition of water molecules.
The same process takes place inside cells through enzymes.
Sucrose + water + hydrolysis = glucose + fructose

Properties of Disaccharides

• Sweet tasting.
• Soluble in water.
• Crystallisable.
• Maltose and lactose are reducing sugars while sucrose is non-reducing sugar.
• Sucrose is the form in which carbohydrate is transported in plants:
• This is because it is soluble and chernically stable.
• Sucrose is a storage carbohydrate in some plants e.g. sugar-cane and sugar-beet.
• Disaccharides are hydrolysed to produce monosaccharide units which are readily metabolised by cell to provide energy.

Polysaccharides

• If many monosaccharides are joined together through condensation, a polysaccharide is formed.
• Polysaccharides may consist of hundreds or even thousands of monosaccharide units.

Examples of polysaccharides:

• Starch - storage material in plants.
• Glycogen is a storage carbohydrate in animals like starch, but has longer chains.
• Inulin - a storage carbohydrate in some plants e.g. Dahlia.
• Cellulose - structural carbohydrate in plants.
• Chitin - forms exoskeleton in arthropods.

Importance and Functions of Polysaccharides
They are storage carbohydrates - starch in plants glycogen in animals.
They are hydrolysed to their constituent monosaccharide units and used for respiration. 
They form structural material e.g. cellulose makes cell walls.
Cellulose has wide commercial uses e.g.

• Fibre in cloth industry.
• Cellulose is used to make paper.
• Carbohydrates combine with other molecules to form important structural compounds in living organisms.

Examples are:
Pectins: Combine with calcium ions to form calcium pectate.
Chitin: Combine with (NH) group. Makes the exoskeleton of arthropods, and walls of fungi.

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1. Define nutrition
2. State the importance of nutrition
3. Differentiate the various modes of feeding
4. Define photosynthesis
5. State the importance of photosynthesis
6. Describe the structure and function of chloroplast
7. Give a word equation for photosynthesis
8. describe briefly the process of photosynthesis in plants
9. describe factors that cause high rate of photosynthesis
10. Give the differences between the light and dark reactions during photosynthesis
11. What are chemicals of life?
12. What are organic compounds?
13. List the organic compounds
14. What are carbohydrates?
15. Name the groups of carbohydrates
16. State the general functions of carbohydrates
17. what are proteins?
18. Name the types of amino acids
19. State the classes of proteins
20. Give the functions of proteins
21. What are lipids
22. Name the types of lipids
23. What are the building blocks of lipids?
24. State the functions of lipids
25. What are enzymes?
26. State the properties of enzymes
27. State the factors that affect enzyme action
28. Name the types of enzyme inhibitors
29. What are the functions of enzymes?
30. Explain the various types of heterotrophic nutrition
31. Differentiate between omnivorous, carnivorous and herbivorous modes of nutrition
32. What is dentition?
33. Distinguish between the terms homodont and heterodont
34. Name the types of teeth found in mammals
35. Describe the adaptations and functions of various types of mammalian teeth
36. Draw a labeled diagram to represent internal structure of a mammalian tooth