Biology Form 1-4 Notes PDF

BIOLOGY FORM ONE NOTES INTRODUCTION TO BIOLOGY What is Biology? Biology is the branch of science that deals with the study of living things. In Greek, Bios means life while Logos means knowledge. Branches of biology There are two main branches: 1. Botany: Study of plants 2. Zoology: Study of a...

BIOLOGY FORM ONE NOTES INTRODUCTION TO BIOLOGY What is Biology? Biology is the branch of science that deals with the study of living things. In Greek, Bios means life while Logos means knowledge. Branches of biology There are two main branches: 1. Botany: Study of plants 2. Zoology: Study of animals The others include: 1. Ecology: Study of living things in their surroundings. 2. Genetics: The study of inheritance and variation. 3. Entomology: Study of insects 4. Parasitology: Study of parasites 5. Taxonomy: Study of classification of organisms 6. Microbiology: Study of microscopic organisms 7. Anatomy: Study of structure of cells 8. Cytology: Study of cells 9. Biochemistry: Study of chemical changes inside living organisms Name at least six other smaller branches of biology (6 marks). Importance of Biology 1. Solving environmental problems e.g. Food shortage, poor health services, pollution, misuse of environmental resources etc. 2. Choice of careers e.g. Medicine, Agriculture, public health, Veterinary, Animal husbandry, Horticulture, Dentistry etc. 3. Acquiring scientific skills e.g. observing, identifying, recording, classification, measuring, analyzing, evaluating etc. 4. International co-operation e.g. Development of HIV\AIDS vaccine, fight against severe Acute respiratory Syndrome (SARS), fight to save ozone layer from depletion, management of resources through international depletion. 1  Others  Help on study of other subjects  Learn what living things are made up of and their bodies work  Acquire knowledge about plant and animal diseases and their treatment.  Know the effects of our bodies on drug and substance abuse and can kill.  Learn about HIV\AIDS diseases and other viral diseases e.g. its treatment—balanced diets, proper hygiene, spreading, sexual behavior, cultural practices etc. List five professional occupations that require the study of biology. (5 marks) Characteristics of living things; 1. Nutrition: Process by which living things acquire and utilize nutrients: plants photosynthesize; animals feed on already manufactured foods. 2. Respiration: energy-producing process occurring in all the cells of living things. 3. Gaseous Exchange: where living things take in air (oxygen) and give out air(carbon iv oxide) across respiratory surfaces. 4. Excretion: Process by which waste or harmful materials resulting from chemical reactions within cells of living things are eliminated. Excess of such materials poison living things. 5. Growth and Development: Growth –is the irreversible increase in size and Mass.—Essential for body function. Development – Irreversible change in complexity of the structure of living things. 6. Reproduction: Process by which living things give rise to new individuals of the same kind. 7. Irritability: Is the ability of living things to perceive changes in their surroundings and respond to them appropriately. E.g. reaction to changes in temperature, humidity, light, pressure and to the presence of certain chemicals. 8. Movement: Change in position by either a part or the whole living thing. Locomotion – Progressive change in position by the 2  whole living thing. In animals, movement include; swimming, walking, running, flying. In plants, closing of leaves, folding of leaves, closing of flowers, growing of shoots towards light etc. Question 1. List four uses of energy obtained from the process of respiration. (4 marks). 2. List six characteristics of living things (6 marks). Collection of specimens Apparatus used 1. Sweep net: for catching flying insects. 2. Fish net: For trapping small fish and other small water animals. 3. Pooter:For sucking small animals from rock surfaces and tree barks. 4. Bait trap: For attracting and trapping small animals e.g. rats. 5. Pit fall trap: For catching crawling animals. 6. Pair of forceps: picking up small crawling animals e.g. stinging insects. 7. Specimen bottles: keeping collected specimen. Larger specimens require large bottles. 8. The magnifying lens: Instrument used to enlarge objects. Lenses are found in microscope and the hand lens (magnifier). Its frame is marked e.g. x8 or x10—indicating how much larger will be the image compared to object. Precautions during Collection and Observation of specimens  Collect only the number of specimen you need.  Do not harm the specimens during the capture or collection exercise.  Handle dangerous or injurious specimens with care e.g. stinging plants or insects i.e. use forceps or hand gloves.  The teacher will immobilize highly mobile animals. (diethyl ether, formalin, chloroform)  Do not destroy the natural habitat of the specimens. Practical activity 2 3 Practical activity 3 Comparison between plants and animals Plants Animals 1. Green in colour( have 1. Lack chlorophyll thus chlorophyll) feed on readymade food. 2. Their cells have 2. Cells lack cellulose cell cellulose cell walls. walls. 3. Respond slowly to 3. Respond quickly. changes in the environment. 4. Lack specialized 4. Have complex excretory excretory organs. organs. 5. Do not move about. 5. Move about in search of food and water. 6. Growth occurs in shoot 6.Growth occurs in all body and root tips.(apical parts9intercalary growth). growth) Revision questions CLASSIFICATION I INTRODUCTION Living things are also known as living organisms. Organisms (forms of life) have distinguishing characteristics and therefore are grouped. The Magnifying lens -Is used for enlarging small objects. (Diagram) Procedure of its use  Place the object on the bench.  Move the hand lens from the object to the eye.  An enlarged image is seen. Drawing magnification = Length of the drawing/ drawing Length Length of the object/Actual Length 4 (Diagram) External features of plants and animals External features of plants i) Rhizoids as in moss plant. ii) Fronds in ferns. iii) Roots, stems, leave, flowers, seeds, fruits, and cones in higher plants. External features of animals i) Tentacles in hydra ii) Feathers in birds iii) Shells in snails iv) Wings in birds v) Fur and hair in mammals vi) Scales and fins in fish vii) Proglotids in tapeworms viii) Mammary glands in mammals ix) Locomotory Structures e.g. limbs in insects x) Body pigmentation Practical activity 1 To collect and observe animal specimens To collect and observe plant specimens What is classification? -Is an area of biology that deals with the grouping of living organisms according to their structure. Organisms with similar structures are put under one group referred to as a taxon—taxa (plural). The groupings also consider evolutionary relationships (phylogeny)— since all living organisms had a common origin at one time. Taxonomy—Science of classification. Taxonomist—Biologist who studies taxonomy. Need for classification. Reasons 5  1. To identify living organisms into their correct groups for reference and study 2. To bring together living organisms with similar characteristics but separate those with different features. 3. To arrange information of living organisms in an orderly manner. This avoids chaos and confusion. 4. To understand the evolutionary relationship between different organisms Taxonomic Units Are groups (taxa) into which organisms are placed as a matter of convenience. Groups are based on observable characteristics common in the group. In a classification scheme (taxonomic units or groups, a hierarchy of groups are recognized starting with the first largest and highest group; the Kingdom to the smallest and lowest unit; the species. There are 7 major taxonomic units. KINGDOM PHYLUM/ DIVISION CLASS ORDER FAMILY GENUS SPECIES The Kingdom There are five Kingdoms of living organisms, namely: 1. Kingdom Monera: bacteria 2. Kingdom protoctista: algae, protozoa, amoeba, paramecium 3. Kingdom Fungi: Moulds, Yeast, Mushrooms 4. Kingdom Plantae: Moss plants, ferns, maize, garden pea, pine, meru oak, bean etc. 5. Kingdom Animalia: hydra, tapeworms, bees, human beings etc. 6 A kingdom is divided into Phyla in animals or divisions in plants and sorts out organisms based on body plan and form. Plan is the adaptation to a special way of life. The Class is further divided into small groups; Orders using structural features. Orders are divided into families using structural features, then Families into Genera (singular genus) –based on recent common ancestral features that are less adaptive. Genus is divided into species i.e. kind of plant, or animal. Down the hierarchy, the number of organisms in each group decreases but their similarities increases. The Species group members naturally interbreed to produce fertile off springs. Minor differences are exhibited in the species groups e.g. on colour of the skin in human beings and varieties of plants. The groups of the species are termed to as varieties, races or strains. Classification of A human being and a maize plant Taxonomic Human being maize bean unit kingdom Animalia plantae plantae Phylum or Chordata Angiospermaphyta Angiospermae division class Mammalia monocotyledonae Dicotyledonae order Primates Graminales Rosales family Hominidae Graminaceae Leguminosae genus homo zea Phaseolus species sapiens mays Vulgaris Scientific name Homo sapiens Zea mays phaseolus vulgaris Scientific Naming Of Living Organisms Present naming was developed by carolus Linnaeus 18th c, where organisms were given 2 names in Latin language. Living organisms have their scientific names and common names i.e. local or vernacular names. 7 Scientific naming uses the double naming system—Binomial system. In binomial system, an organism is given both the genus and species name. Binomial nomenclature (Double –naming system)-Is the assigning of scientific names to living organisms governed by a definite set of rules recognized internationally. Principles of binomial nomenclature a) The first, genus name, should begin with a capital letter and the second name, species, should begin or written in small letters e.g. Lion---- Panthera leo Leopard----- Panthera pardus Domestic dog----- Canis farmiliaris Human being--- Homo sapiens Maize plant---Zea mays Lion and Leopard are closely related ---Same genus but distantly related—different species. b) The scientific names must be printed in italics in textbooks and where hand written to be underlined e.g. Panthera leo. c) The specific name (species) is frequently written with the name of the scientist who first adequately described and named the organism e.g.Phaseolus vulgaris i.e. Vulgaris is the scientist who described and named the bean plant. d) Biologists should give a Latinized name for a newly described animal or plant species where Latin name is missing e.g. Meladogyne kikuyuensis – Is a scientific name of a nematode from kikuyu. Aloe kilifiensis --- A member of Aloeceae family from Kilifi discovery. Garinsoga parviflora waweruensis --- a member of Macdonald eye family discovered by Waweru. Study Question 1 Complete the table below Taxon Lion Domestic Garden Napier dog pea grass kingdom 8  Phylum/division class order family genus species Scientific name --------------------- ------------------------ -- --------------------- ------------------------ Revision Questions: CLASSIFICATION 1  Review of the magnification lens  Calculating Magnification  External characteristics of plants and animals Diversity of Living Organisms  Organisms with similar characteristics are placed under one group called taxon (taxa).  The science of classification is known as taxonomy.  Biologists who study taxonomy are called taxonomists. Need For Classification 1. Help in identifying living organisms into their correct groups for reference. 2. It brings together organisms with similar characteristics and separates those with different features. 3. Help to organize information about living organisms in an orderly manner avoiding any confusion. 4. Help to understand the evolutionary relationship between different living organisms. Historical Background of Classification  Long time ago classification was artificial where living things were classified as either plants or animals.  Plants were classified as herbs, shrubs and trees.  Animals were further divided into carnivores, herbivores and omnivores. 9   Today modern classification uses evolutionary relationships between living organisms. Taxonomic Units of Classification  This refers to the groups into which living organisms are placed in classification.  These units start from the first largest and highest group (kingdom) to the smallest and lowest unit (species).  There are seven taxonomic units as shown below. Kindom Phylum(division) Class Order Family Genus Species 1. Kingdom Carolus Linnaeus (1707-1778) initially introduced the two kingdom system of classification. However many new life forms have been discovered which are neither animals nor plants. This has led to a more accepted classification system that adopts five kingdoms. These are; i.) Monera.eg bacteria ii.) Protoctista e.g algae and protozoa iii.) Fungi e.g. mushrooms, moulds and yeast. iv.) Plantae e.g. maize, ferns and all types of trees. v.) Animalia e.g. man, cow tapeworm, flies etc. Kingdom is further divided into several phyla in animals or divisions in plants. 2. Phylum (phyla) or Division in plants. It is the second largest and further divided into classes. 3. Class Each class is divided into several orders. 4. Order 10  Orders are divided into smaller groups called families. 5. Family Family is divided into several Genera. 6. Genus Here members are closely related. It is further divided into the species. 7. Species This is the smallest unit of classification. Species is defined as a group of organisms whose members naturally interbreed to produce fertile offspring’s. Members of a given species have small differences such as skin colour, height etc. Classification of Man and Maize plant. ( Table 2.1 Page 15 KLB Bk 1) Scientific Naming of Living Organisms.  Today organisms are given two names in Latin language. This was developed by Carolus Linnaeus.  Latin language was used because it was widely spoken during his time.  In scientific naming, an organism is given the genus and the species name.  This double naming system is known as Binomial system (two name System) Binomial Nomenclature. This is the double naming system of organisms where organisms are assigned two names i.e. the generic name and the specific name. In binomial nomenclature the following rules are observed. i.) Generic name is written first followed by the specific name. First letter in the generic name is in capital and the rest are in small letters. Specific name is written in small letters. ii.) The two names are underlined separately when handwritten or italicised when printed. iii.) Newly discovered species must be given Latinized names. iv.) Specific name is frequently written with the name of the scientist who first adequately described and named the organism. 11 Examples Revision Questions CELL PHYSIOLOGY  This is the study of the functions of cell structures. Membrane Structure and Properties  A membrane is a surface structure which encloses the cell and organelles. Membranes regulate the flow of materials into out of the cell or organelle.  Examples of membranes: cell membrane, tonoplast (membrane surrounding the vacuole), nuclear membrane, mitochondrial membrane, chloroplast membrane etc. The Cell Membrane  It has three layers, two protein layers and a phos-pholipid layer sandwiched in between the two. Diagram Properties of Cell Membrane 1. Semi-permeability. – It has small pores allowing for the passage of molecules of small size into and out of the cell. Cell Wall however allows all materials to pass through it hence it is referred to as being Permeable. 2. Sensitivity to Changes in Temperature and pH – Extreme temperature and pH affects the cell membrane since it has some protein layers. Such changes alter the structure of the membrane affecting its normal functioning. 3. Possession of Electric Charges – it has both the negative and positive charges helping the cell to detect changes in the environment. These charges also affect the manner in which substances move in and out of the cell Physiological Processes  The ability of the cell to control the movement of substances in and out of the cell is achieved through physiological processes such as Diffusion, Osmosis and Active Transport. 12 Diffusion  This is a process by which particles move from a region of high concentration to a region of low concentration. Practical Activity 1 To demonstrate diffusion using potassium permanganate (VII)  The difference in concentration of particles between the region of high concentration and the region of low concentration is known as the diffusion gradient. Role of Diffusion in Living Organisms 1. Absorption of Materials  Mineral salts in the soil enter the root by diffusion since their concentration in the soil is greater than in the root hair cells.  Digested food (glucose and amino acids) diffuse across the wall of the ileum into the blood for transport to rest of the body. 2. Gaseous Exchange in Plants and Animals  In both plants and animals, respiratory gases (oxygen and Carbon (IV) oxide) are exchanged through simple diffusion depending on their concentration gradient. 3. Excretion of Nitrogenous Wastes 4. Transport of Manufactured Food form Leaves to other Plant Parts. 5. Factors Affecting Diffusion a) Diffusion Gradient  A greater diffusion gradient between two points increases the rate of diffusion. b) Surface Area to Volume Ratio  The higher the ratio the greater the rate of diffusion and the lower the ratio the lower the rate.  This means that small organisms expose a large surface area to the surrounding compared to large organisms.  Small organisms therefore depend on diffusion as a means of transport of foods, respiratory gases and waste products. Diagrams 13  c) Thickness of Membranes and Tissues  The thicker the membrane the lower the rate of diffusion because the distance covered by the diffusing molecules is greater. The thinner the membrane, the faster the rate.  Size of the Molecules  Small and light molecules diffuse faster than large and heavy molecules. d) Temperature  Increase in temperature increases the energy content in molecules causing them to move faster. Osmosis  This is the process where solvent molecules (water) move from a lowly concentrated solution (dilute) to a highly concentrated solution across a semi-permeable membrane. Diagram fig 4.6  The highly concentrated solution is known as Hypertonic Solution.  The lowly concentrated solution is called Hypotonic solution.  Solution of the same concentration are said to be Isotonic.  Osmosis is a special type of diffusion because it involves the movement of solvent (water) molecules from their region of high concentration to region of low concentration across a semi permeable membrane. Practical activity 2 Practical activity 3 Osmotic Pressure  This is the pressure which needs to be applied to a solution to prevent the inward flow of water across a semi permeable membrane. This is the pressure needed to nullify osmosis.  Osmotic pressure is measured using the osmometer. Osmotic Potential  This is the measure of the pressure a solution would develop to withdraw water molecules from pure water when separated by a semi permeable membrane. 14 Water Relations in Animals  Cell membrane of the animal cell is semi permeable just like the dialysis/visking tubing.  Cytoplasm contains dissolved sugars and salts in solution form.  If an animal cell e.g. a red blood cell is placed in distilled water (hypotonic solution), water flows in by osmosis.  The cell would swell up and eventually burst because the cell membrane is weak. The bursting of the red blood cell when placed in hypotonic solution is called Haemolysis.  If a similar red blood cell is placed in a hypertonic solution, water is drawn out of the cell by osmosis. The cell will shrink by a process called Crenation.  Body fluids surrounding the cells must therefore have same concentration as to that which is found inside the cell. Diagrams Water Relations in Plants  When a plant cell is placed in a hypotonic solution it gains water by osmosis and distends outwards.  As the cell gains more water, its vacuole enlarges and exerts an outward pressure called turgor pressure. As more water is drawn in, the cell becomes firm and rigid and is said to be turgid.  The cell wall in plant cell is rigid and prevents the cell from bursting unlike the case in animal cells.  The cell wall develops a resistant pressure that pushes towards the inside. This pressure is equal and opposite the turgor pressure and is called wall pressure. Diagrams  When a plant cell is placed in hypertonic solution, water molecules move out of the cell into the solution by osmosis. The cell shrinks and becomes flaccid.  If the cell continues to lose more water, plasma membrane pulls away from the cell wall towards the center. 15   The process through which plant cells lose water, shrink and become flaccid is called plasmolysis.  Plasmolysis can be reversed by placing a flaccid cell in distilled water and this process is called deplasmolysis. Study Question 5 Practical Activity 4 Wilting  When plants lose water through evaporation and transpiration, cells lose turgidity, shrink and the plant droops. This is called wilting.  If water supply from the soil is inadequate, plants do not recover hence permanent wilting. Study Question 6 Role of Osmosis in Organisms 1. Absorption of water from the soil  Root hair cells of plants absorb water from the soil by osmosis. 2. Support  Cells of herbaceous plants, which are less woody, absorb water, become turgid hence support. 3. Opening and closing of the stomata  During the day, guard cells synthesize glucose, draw in water, become turgid hence open the stomata.  During the night, they lose turgidity since there is no photosynthesis. As a result, they shrink thus closing the stomata. 4. Feeding in insectivorous plants  These plants are able to change their turgor pressure on the leaves which close trapping insects which are digested to provide the plant with nitrogen. 5. Osmoregulation  In the kidney tubules, water is reabsorbed back to the body by osmosis. 16 Factors Affecting Osmosis i.) Concentration of Solutions and Concentration Gradient. The greater the concentration gradient between two points, the faster the rate of osmosis. ii.) Optimum Temperature as long as it does not destroy the semi-permeability of the membrane. Active Transport  This is the process that moves substances across cell membranes against a concentration gradient.  This process requires energy to move these substances across cell membranes and involves carriers.  Substances such as amino acids, sugar and many ions are taken in by living organisms through active transport. Role of Active Transport i.) Re-absorption of sugars and useful substances by the kidney ii.) Absorption of some mineral salts by plant roots iii.) Absorption of digested food from the alimentary canal into the blood stream iv.) Accumulation of substances in the body to offset osmotic imbalance in arid and saline environment v.) Excretion of waste products from body cells Factors Affecting Active Transport. i.) Oxygen concentration. ii.) Change in pH. iii.) Glucose concentration. iv.) Temperature. v.) Enzyme inhibitors. NB/ Any factor affecting energy production affect the rate of active transport. Revision Questions. Cell Specialization, Tissues, Organs and Organ Systems 1. Cell specialization  This is where cells are modified to perform specific functions. Such cells are said to be specialized. 17   Examples include the sperm cell which has tail for swimming and the root hair cell which is extended creating large surface area for water absorption. 2. Tissues.  These are cells of a particular type that are grouped together to perform the same function. Animal tissues include; - Epithelial tissue – which is a thin continuous layer of cells for lining and protection of internal and external surfaces. - Skeletal – it is a bundle of elongated cells with fibres that can contract. Its contraction and relaxation brings about movement. - Blood tissue – this is a fluid containing red blood cells, white blood cells and platelets. It transports many substances and protects the body against infections. 18  - Connective tissue – made up of strong fibres that connect other tissues and organs holding them together. Plant tissues include: - Epidermal tissue of a plant – this is a single layer of cells protecting the inner tissues of the plant. - Palisade tissue – this is a group of cells rich in chloroplasts containing chlorophyll. They absorb light energy during photosynthesis. - Parenchyma tissue – it is made thin walled irregularly shaped cells. They store water and food. - Vascular bundle – consists of the xylem and phloem. Xylem conducts water and mineral salts while phloem conducts food substances. 19  3. Organs  Many tissues become specialized and grouped together to perform a functional unit called the organ.  Examples of organs in plants include; roots, leaves, flowers and stem.  In animals they include heart, lungs, kidney, brain, stomach and the liver. 4. Organ systems.  This is made of several organs whose functions are coordinated and synchronized to realize an effective action is called an organ system. Examples include; digestive, circulatory, excretory, respiratory, reproductive and nervous system. Revision Questions MICROSCOPE Microscope Parts & Function Parts of the Microscope 1. Contains a Eyepiece magnifying lens that focuses the image from the objective into your eye. 2. Course For focusing Adjust under low magnification 3. Fine For focusing Adjust under high magnification or low 4. Low For large Power specimens or Objective overview 20  5. High For detailed Power viewing or small Objective specimens 6. What you want Specimen to look at on glass slide 7. Stage Supports specimen in correct location to lens 8. Focuses the light Condenser on specimen 9. Regulates Diaphragm amount of light (iris or and contrast disc) 10. Light Illuminates the Source specimen for viewing Handling and Care of the Microscope The following rule should be observed: 1. Use both hand when carrying the microscope. One hand should hold the base and the other holds the limb. 2. Never place the microscope too close to the edge of the bench. 3. Do not touch the mirror and the lenses with the fingers. 4. Clean dirty lenses using soft tissue. 5. Clean other parts using a soft cloth. 6. Do not wet any part of the microscope. 21  7. Make sure the low power clicks into position in line with the eye piece before and after use. 8. Always store the microscope in a safe place free from dust and moisture. Using the Microscope 1. Place microscope on the bench with the stage facing away from you. 2. Turn the low power objective lens until it clicks into position. 3. Ensure the diaphragm is fully open. 4. Look through the eyepiece with one eye. Adjust the mirror to ensure maximum light can pass through. 5. Place the slide containing the specimen on the stage and clip it into position. Make sure the slide is at the centre of the field of view. 6. Again look through the eyepiece while adjusting the mirror to ensure maximum light reach the specimen. 7. Use the coarse adjustment knob to bring the low power objective lens to the lowest point. While viewing through the eyepiece, turn the coarse adjustment knob gently until the specimen comes into focus. 8. Use the fine adjustment knob to bring the image into sharp focus. 9. Make a drawing of what you see. 10. For higher magnification, turn the medium power into position and adjust the focus using the coarse knob. Use the fine adjustment knob for sharper focus. 11. For even large magnifications, turn the high power objective lens into position. In this case use only the fine adjustment knob to bring details into sharper focus. Magnification  Magnification of the object viewed under the microscope is calculated by; Magnification = Eye Piece Lens Magnification X Objective Lens Magnification. 22   If the eyepiece lens has the magnification of x5 and the low power objective lens has a magnification of x10, the total magnification is 5x10=50. Study Question 1 Fill the table below. Eye piece lens Objective lens Total magnification maginification magnification X5 X4 X10 X5 X10 X100 X40 X600 X10 X100 Practical Activity 1 Cell Structures as Seen Under the Light Microscope  The following cell organelles can be seen under the light microscope. - Cell wall. - Cell membrane - Cytoplasm - Nucleus - Vacuole. - Chloroplasts. Diagrams- plant and animal cells The Electron Microscope.  It is more powerful than the light microscope.  It can magnify up to 500,000 times and has high resolving power.  The high resolving power of the electron microscope enables it to separate objects which lie close to one another.  Electron microscope uses a beam of electrons instead of light to illuminate the object. Study Question 2 Practical Activity 2 Cell Structures as Seen Under the Electron Microscope 23 Diagrams – Plant and Animal Cells The Cell Organelles i) Cell membrane (Plasma Membrane).  It has three layers i.e. one layer of phospho-lipid layer sandwiched between two protein layers.  It is flexible with pores and ahs the following main functions. a) Encloses all the cell contents. b) It allows selective movement of substances into and out of the cell since it is semi-permeable. Diagram ii) Cytoplasm  It is s fluid medium in which chemical reactions take place.  It has some movement called cytoplasmic streaming.  It contains organelles, starch, glycogen, fat droplets and other dissolved substances. iii) Nucleus  It has double membrane called the nuclear membrane.  The membrane has pores allowing passage of materials into and out of the cell.  Nucleus has a fluid called nucleoplasm in which the nucleolus and chromatin are suspended.  Nucleolus manufactures ribosomes while chromatin contains the hereditary material. iv) Mitochondria(Mitochondrion)  They are sausage shaped and are the respiratory sites.  Mitochondrion has two membranes. Inner membrane is greatly folded into cristae to increase the surface area for respiration.  Cells that require a lot of energy have large number of mitochondria e.g. muscle cell, sperm cell, kidney cell etc. Diagram v) Endoplasmic Reticulum (ER) 24  Some endoplasmic reticulums have granules called Ribosomes on their surfaces hence referred to as rough endoplasmic reticulum.  Others do not contain ribosomes hence the name smooth endoplasmic reticulum.  Rough endoplasmic reticulum transport proteins while the smooth endoplasmic reticulum transports lipids. Diagrams vi) Ribosomes  They are spherical in shape and form the site for protein synthesis. vii) Lysosomes  They contain lytic enzymes which break down large molecules, destroy worn out organelles or even the entire cell. viii) Golgi Bodies (Golgi apparatus)  Their function is to package and transport glyco-proteins.  They are also associated with secretion of synthesized proteins and carbohydrates. Diagram ix) Centrioles  They are rod shaped structures that are used in cell division and in the formation of cilia and flagella.  Plant cells lack the Centrioles. x) Chloroplasts  They are egg shaped and contain two membranes.  Chloroplast has chlorophyll which traps light energy to be used during photosynthesis. xi) Vacuoles  This are sacs filled with a fluid called cell sap.  Animal cells contain small vacuoles while plant cells have large vacuoles.  Sap vacuoles store sugars and salts.  Food vacuole store and digest food while contractile vacuoles excrete unwanted materials from the cell. xii) Cell wall 25   It is a rigid outer cover of the plant cells made of cellulose.  It gives the plant cell a definite shape while providing mechanical support and protection.  Cell wall also allows water, gases and other materials to pass through it. Study Question 3 Differences between Plant and Animal Cells Preparation of Temporary Slides Practical Activity 3 Estimation of Cell Sizes. NUTRITION IN PLANTS AND ANIMALS Nutrition  This is the process by which organisms obtain and Assimilate nutrients.  There are two modes of nutrition; Autotrophism and Heterotrophism. Autotrophism  This is where living organism manufacture its own complex food substances from simple substances such as carbon (iv) oxide, water, light or chemical energy.  Where sunlight is used as a source of energy, the process is referred to as photosynthesis.  Photo means light while synthesis means to make.  Some none green plants make their own food using energy obtained from certain chemicals through a process called chemosynthesis.  Organisms that make their own food are referred to as autotrophs. Heterotrophism 26   This is where organisms take in complex food materials such as carbohydrates, proteins and fats obtained from bodies of plants and animals.  Organisms that feed on already manufactured foods are called Heterotrophs. Autotrophism External Structure of a Leaf A leaf is a flattened organ which is attached to the stem or a branch of a plant. Diagrams Parts of a leaf Lamina: This is the flat surface. It is green in colour and contain the photosynthetic tissue. Midrib: This is a thick structure running through the middle of the leaf Veins: They arise from the midrib to forming an extensive network of veins. Leaf Apex: This is the tip of the leaf and usually it is pointed. Petiole: It attaches the leaf to the stem or branch. In some monocotyledonous plants the leaves are attached to the stem by the leaf sheath. Practical Activity 1: To examine the External Features of a Dicotyledonous and Monocotyledonous leaf Study Question 1 Internal Structure of a Leaf  Internal structure of the leaf is composed of the following parts. i.) Cuticle.  It is a thin waterproof and transparent layer that coats the upper and lower surfaces of the leaf.  It reduces excess water loss and protects the inner tissue of the plant against mechanical injury.  It also prevents entry of disease causing micro organisms.  Since it is transparent, it allows penetration of light for photosynthesis. ii.) Epidermis. 27  It is a one cell thick tissue on both the upper and lower leaf surfaces.  It secretes the cuticle and also protects the inner tissues from mechanical damage and prevents entry of pathogens.  Epidermal cells have no chloroplast except the guard cells.  Guard cells are special bean shaped cells. They have chloroplast and are able to carry out photosynthesis hence controlling the opening and closing of the stomata.  Air moves into and out of the leaf through the stomata. iii.) Palisade layer.  This is layer of cells located beneath the upper epidermis.  It is made of cylindrical shaped cells closely packed together. They have numerous chloroplasts containing chlorophyll.  Their position and arrangement enables them to receive maximum light. iv.) Spongy Mesophyll Layer.  This is below the palisade layer. The cells are irregularly shaped and loosely packed creating large air spaces in between them.  The air spaces allow gases to diffuse in between the cells. They contain fewer chloroplasts as compared to the palisade cells. v.) Leaf Veins.  Each vein is a vascular bundle consisting of xylem and phloem.  Xylem conducts water and mineral salts from the roots to the leaves while the phloem translocates manufactured food from the leaves to the rest of the plant. 28 Study Question 2 Adaptations of Leaves to Photosynthesis. 1. Broad and flat lamina to increase surface area of Carbon (IV) oxide and sunlight absorption. 2. Thin transparent cuticle and upper epidermis; to allow easier penetration of light to photosynthetic cells; 3. Thin; for faster diffusion of gases; 4. Palisade cells placed next to the upper surface; to trap maximum light for photosynthesis; 5. Palisade cells with numerous chloroplasts; to trap maximum amount of light for photosynthesis; 6. Large/ intercellular air spaces in the spongy mesophyll layer; for storage of Carbon (IV) oxide for easier gaseous exchange; 7. Waxy water proof cuticle; to reduce water loss sand reflect excess light; 8. Leaf mosaic/ non-overlapping leaves; for maximum exposure to light; 9. Guard cells, modified cells to open and close stomata; to control amount of water loss from the leaf and allows gaseous exchange; 10. Leaves have leaf veins; xylem to conduct water to photosynthetic cells, Phloem to translocate products of photosynthesis to other parts of plant; The Chloroplast  They are disc shaped organelles found in the cytoplasm of plant cells.  Each chloroplast has a double membrane; the inner and outer membrane.  Chloroplasts are made of layers of membranes called lamellae contained in a fluid matrix called stroma.  Several lamellae come together to form the granum (grana).  Granum contains chlorophyll molecules and other photosynthetic pigments. 29   The stroma contains enzymes that speed up the rate of photosynthesis. Practical Activity 2: To Observe Distribution of Stomata Study Question 3. The Process of Photosynthesis  The raw materials for photosynthesis are; water and carbon (IV) oxide. The process however requires the presence of sunlight energy and chlorophyll pigment.  The products of photosynthesis are glucose and oxygen. The process can be summarized using an equation as shown below. 6H2O + 6CO2 ----------> C6H12O6+ 6O2 Water + Carbon (IV) oxide Glucose + Oxygen. The above chemical equation translates as: Six molecules of water plus six molecules of carbon (IV) Oxide produce one molecule of sugar plus six molecules of oxygen  The process of photosynthesis is however more complex than shown in the above equation and can be divided into two stage; the light and dark stages. Light stage (Light Dependent Stage) - Occurs in the grana containing chlorophyll which traps / absorbs sun light energy. - This Energy is used to split water molecules into hydrogen ion and oxygen gas. - This process is called photolysis of water and is shown below. LIGHT ENERGY 2H2O 4H + O2 CHLOROPHYLL 30  (Water) Hydrogen atom Oxygen - Hydrogen atoms produced here enter into the dark stage. - Oxygen gas removed through stomata or is used for respiration within the plant; - Some Light energy is used in Adenosine Triphosphate (ATP) formation; ATP an energy rich compound. - ATP is later used in the dark stage. Dark stage. (Light Independent Stage) - Carbon (IV) oxide combines with hydrogen atoms to form glucose/simple carbohydrate. - This is called Carbon (IV) Oxide fixation. Carbon (IV) oxide + Hydrogen Atom Simple Carbohydrate CO2 + 4H C6H12O6 - This stage takes place in the stroma and proceeds whether light is present or not. - ATP Energy from light stage is used to provide the required energy in this reaction; - Simple sugars formed are used for respiration to provide energy or are converted to storable forms e.g lipids, proteins, starch, cellulose, etc. Study Question 4 Practical Activity 3: To Investigate the Presence of Starch in a Leaf. Study Question 5 Factors Affecting the Rate of Photosynthesis i.) Light Intensity.  Increase in light intensity increase the rate of photosynthesis up to a certain level where it slows down and finally levels off.  Very bright sunshine may damage the plant tissues due to high amount of ultra violet light.  Light quality or light wavelength also affects the rate of photosynthesis. 31  Red and blue wavelengths of light are required by most plants for photosynthesis. Rate of Photosynthesis Range of optimum light intensity Light intensity ii.) Carbon (IV) oxide concentration  Increase in Carbon (IV) oxide concentration increases the rate of photosynthesis linearly up to a certain level after which it slows down and levels off. Rate of Photosynthesis Range of optimum CO2 concentration 32 Carbon (IV) oxide concentration iii.) Temperature  Photosynthesis is an enzyme controlled process, therefore increase in temperature increase the rate of photosynthesis up to the optimum temperature.  Increase in temperature beyond the optimum decreases the rate sharply as the enzymes become denatured. iv.) Water  Plants need water for photosynthesis. Hydrogen atoms required in the dark stage during Carbon (IV) oxide fixation are derived from water during photolysis. Study Question 6 Practical Activity 4: To Investigate Factors Necessary for Photosynthesis. a) Light Study Question 7 b) Carbon (IV) oxide. Study Question 8 c) Chlorophyll. Study Question 9 Study Question 10 Practical Activity 5: To Investigate the Gas Produced During Photosynthesis. Study Question 11 33 Chemical Compounds Which Constitute Living Organisms  Cells, tissues and organs are made of chemicals which are referred to as chemicals of life.  The study of chemical compounds found in living organisms and reactions in which they take part is called Biochemistry.  Chemicals of life include carbohydrates, lipids and proteins. a) Carbohydrates  They are compounds of carbon, hydrogen and oxygen in the ratio of 1:2:1 respectively.  Carbohydrates have a general formula of (CH2O)n where n represents the number of carbon atoms in a molecule of carbohydrate.  Carbohydrates are divided into three groups; Monosaccharide’s, Disaccharides and Polysaccharides. i) Monosaccharides  They are the simplest carbohydrates and have a general chemical formula of (CH2O)n where n = 6.  Their chemical formular is therefore C6H12O6. They include; glucose, fructose, galactose etc. Properties of Monosaccharides i) They are soluble in water to form sweet tasting solutions. ii) They are crystalissable. iii) They have the reducing property where they reduce copper sulphate in Benedicts solution to red copper (I) oxide. Functions i) They are oxidized to release energy during respiration. ii) When condensed together, they form polysaccharides such as starch, cellulose or glycogen. ii) Disaccharides  They are formed by linking two Monosaccharide molecules through the process of condensation where a molecule of water is liberated. Condensation 34 Monosaccharide + Monosaccharide Disaccharide + Water. C6H12O6 + C6H12O6 C6H22O11 + H 2O Examples Glucose + Glucose Maltose + Water. Glucose + Fructose Sucrose + Water Glucose + Galactose Lactose + Water.  The type of disaccharide formed depends on the monosaccharide units that condense together. Properties of Disaccharides i) Soluble in water to form sweet tasting solutions ii) They are non reducing sugars. Some such as the maltose can reduce copper sulphate in Benedict’s solution when heated together and are therefore referred to as complex reducing sugars. iii) They are readily broken into their constituent monosaccharide molecules in a process known as Hydrolysis in the presence of water. Hydrolysis Disaccharide + Water Monosaccharide + Monosaccharide C6H22O11 + H 2O Hydrolysis C6H12O6 + C6H12O6 Sucrose + Water Hydrolysis Glucose + Fructose Lactose + Water Hydrolysis Glucose + Galactose Maltose + Water Hydrolysis. Glucose + Glucose. 35   Naturally disaccharides are hydrolyzed by enzymes. In the laboratory, hydrolysis is achieved by boiling them in dilute Hydrochloric acid. Functions  They are hydrolyzed by enzymes into monosaccharide’s which are then oxidized to produce energy. iii) Polysaccharides.They are made of many monosaccharide molecules hence are long and more complex.  They have a general formula of (C6H10O5) n; where the value of n is a very large number. Examples of polysaccharides i) Starch  It is present as stored food in plant tissues e.g. maize, wheat, potatoes, rice etc. ii) Cellulose  This is the component of the cell wall in plants. Cellulose gives the plant cells their definite shape. iii) Glycogen  This is the form in which carbohydrates are stored in animal tissues. Excess glucose is converted into glycogen for storage in the liver. Properties of Polysaccharides i) All are insoluble in water. ii) Do not have a sweet taste hence are referred to as non-sugars. Study Question 12 Practical Activity 6: To Carry out Food Tests for Carbohydrates i) Starch ii) Reducing sugars iii) Non Reducing Sugars b) Lipids  These are the fats and oils. Fats are found in animals while oils are found in plants.  Oils are liquid while the fats are solid at room temperature. 36   They contain carbon, hydrogen and oxygen just like the carbohydrates. However they contain fewer number of oxygen atoms than in carbohydrates.  Lipids are made up of three fatty acid molecules and one molecule of Glycerol.  The nature of a lipid formed, depends on the fatty acids it contains. Glycerol remains the same in all lipids. Diagram  Complex lipids are formed through condensation of many lipid molecules just like in carbohydrates.  Examples of complex lipids include; phospholipids, waxes, steroids and cholesterol.  Presence of lipids in a food sample is detected using the grease spot test or emulsion test. Properties of Lipids 1. When fats are heated they change into liquid while oils solidify under low temperature. 2. Both fats and oils are insoluble in water. They however dissolve in organic solvents such as alcohol to form emulsions and suspensions. 3. Lipids are inert hence can be stored in the tissues of organisms. Functions of Lipids i) Source of energy  They give almost twice as much energy as the Monosaccharides. ii) Source of metabolic water  When oxidized, lipids release more water than Monosaccharides. Such water is referred to as metabolic water. iii) Structural compounds  Lipids are constituents of plasma membrane and protoplasm. iv) Heat insulation  Fats are deposited under the skin of animals forming the adipose tissue which acts as a heat insulator.  Mammals in the temperate regions have thick adipose tissue to greatly reduced heat loss. 37   Thick adipose tissue in aquatic animals helps them to be buoyant in water. v) Protection  Fat is deposited around the major organs such as kidney, heart etc where they act as shock absorber.  Wax in plant cuticles reduces excessive water loss. Study Question 13 Practical Activity 7: testing for the Presence of Lipids i) The Grease Spot ii) The Emulsion Test c) Proteins  Like carbohydrates and lipids, proteins are compounds of carbon, hydrogen and oxygen.  In addition they contain nitrogen and sometimes phosphorous and sulphur.  Some proteins such as haemoglobin contain other elements such as iron.  Proteins are made up of small units called amino acids. There are about 20 different types of amino acids.  All amino acids contain the amino group (-NH2) which consists of hydrogen and nitrogen.  Two amino acids combine to form a dipeptide molecule through the process of condensation.  The bond between two amino acids is called peptide Bond. Many amino acids join together to form a long protein chain called polypeptide chain.  The type and sequence of amino acids contained in such a chain determine the uniqueness of the protein being formed. Properties of Proteins i.) They dissolve in water to form colloidal suspensions (not true solutions) where particles remain suspended in water. ii.) They are denatured by temperatures above 40 0C. Heat alters the structure of the protein molecule. Chemicals such as detergents, acids, bases and organic solvents also denature proteins. 38  iii.) They are amphoteric whereby they have both acidic and basic properties. This property enables them to combine with non-protein compounds to form conjugated proteins such as mucus, and haemoglobin. In mucus the non protein compound is a carbohydrate while in haemoglobin, iron is a non protein. Functions of Proteins i.) Structural Functions  Proteins make the framework of living systems e.g. plasma membrane, connective tissues, muscle fibres, hair, nails, hooves, skeletal materials etc. ii.) Metabolic Regulators  These are divided into two a) Enzymes  Enzymes are organic catalysts which speed up the rate of metabolic reactions such as respiration, photosynthesis, digestion etc. b) Hormones  They are chemical messengers which regulate many body processes such as growth, reproduction, amount of sugars, salts and water in the blood etc. iii.) Source of Energy  Under extreme starvation, proteins are broken down to release energy. Study question 14 Practical Activity 8 To Test for Proteins Enzymes  They are organic catalysts which are protein in nature. They speed up or slow down the rate of chemical reactions in the body without themselves being used up.  They are divided into two; a) Extracellular Enzymes  Extracellular enzymes are produced within the cells but are used outside the cells which produce them e.g. the digestive enzymes. 39  b) Intracellular Enzymes  They are secreted and used within the cells which produce them e.g. the respiratory enzymes. Naming of the Enzyme  There are two methods on naming enzymes; i) Trivial Naming  Enzymes are given names of persons who discovered them.  The names end in -in such as pepsin, trypsin ptyalin etc. ii) Use of suffix –ase  This is the modern method of naming. The suffix –ase is added to the substrate (type of food) or the reaction the enzyme catalyzes. Example 1 Substrate Enzyme Carbohydrate Carbohydrase Starch e.g. amylose Amylase Sucrose Sucrase Maltose Maltase Protein Protease Lipid Lipase Example 2 Reaction Enzyme Hydrolysis Hydrolase Oxidation Oxidase Reduction Reductase Properties of Enzymes 1. They are protein in nature hence are affected by changes in temperature and pH. 2. They are substrate specific. 3. They are efficient in small amounts as they are not affected by the reactions they catalyze. They can be used again and again. 4. They are catalysts that speed up the rate cellular reactions and are not used up in the reactions they catalyses. 5. Most of the enzyme controlled reactions are reversible. 40 Factors Affecting the Rate of Enzyme Controlled Reactions i.) Temperature  Enzymes are sensitive to changes in temperature and pH since they are protein in nature.  Enzymes work best within a narrow range of temperature called the optimum temperature.  Above the optimum temperature, reaction decreases sharply as the enzymes are denatured.  Most enzymes have optimum temperature between 35-40oC.  Very low temperature inactivates the enzymes hence decrease rate of reaction. Diagrams ii.) pH  Most enzymes have a pH of close to 7.  Some however work best in acidic pH e.g. pepsin while others work best in alkaline conditions.  As pH changes from the optimum, enzyme activity decreases.  Extreme acidity or alkalinity denatures most enzymes. Diagrams iii.) Specificity  Enzymes are specific in nature where a particular enzyme acts on a particular specific substrate.  For example, sucrose works on sucrose and not any other substrate. iv.) Substrate Concentration and Enzyme Concentration.  When substrate concentration increases, the rate of enzyme reaction also increases upto a certain level.  Further increase does not increase the rate of reaction as all the active sites of an enzyme are occupied.  When enzyme molecules are increased, the rate of reaction increases proportionally. Diagrams v.) Enzyme Co-factors and Co-enzymes 41   Co-factors are non protein substances which activates enzymes. They are required in small quantities and they include metallic ions such as those of iron, magnesium, zinc, copper etc. Some are vitamins.  Co-enzymes are non protein molecules that work in association with particular enzymes. Most co-enzymes are derived from vitamins. vi.) Enzyme Inhibitors  Inhibitors compete with the normal substrate for the active sites and they take up the active site of the enzyme permanently.  There are two types of inhibitors; a) Competitive Inhibitors  These are chemicals closely related to normal substrate and they compete for active sites with the normal substrate. They slow down the rate of reaction. b) Non Competitive Inhibitors  They do not compete with the substrate. They combine permanently with enzyme molecules thus blocking the active sites. They include poisons such as cyanides, mercury and silver- arsenic compounds. Importance of Enzymes  Enzymes speed up the rate of cellular reactions and also control them. This way, they help prevent violent reactions in the cells. Study Question 15 Practical Activity 9 Study Question 16 Study Question 17 Practical Activity 10 42 FORM TWO BIOLOGY NOTES EXCRETION AND HOMEOSTASIS Excretion-Process by which living organisms separate and eliminate waste products formed during metabolic processes from the body. They include; carbon IV oxide, excess water and mineral salts, nitrogenous wastes etc. accumulation of these substances may become toxic to cells. Homeostasis-This is the maintenance of internal environment of cells under constant conditions E.g. temperature, osmotic pressure, blood sugar and chemical constituents. Egestion. - This is the removal of undigested and indigestible materials from the alimentary Canal of animals. Secretion. - This is the release of certain useful substances produced by cells e.g. hormones, Enzymes, sebum, saliva and mucus. Excretion in Plants  Plants do not have complex organs for excretion because; i. There is very little accumulation of toxic wastes such as nitrogenous wastes. ii. Some waste products are re-used in the same plant such as Co2, oxygen and water. iii. Some of these gases are removed by simple diffusion through the stomata and lenticels. iv. Some plants store wastes in their tissues in non-toxic forms such as nicotine, caffeine, tannins, resins, quinine, morphine etc. Economic Importance of Plant Excretory Products i. Tannins – They are deposited in dead tissues of wood and barks of trees e.g. in acacia and wattle tree. Tannin is used to treat leather. ii. Caffeine – it is stored in coffee berries and tea leaves. It is used as a stimulant. iii. Quinine – it is stored in the leaves of aloe and bark of cinchona tree. It is used in the treatment of malaria. 43  iv. Cocaine – it is obtained from the leaves of coca plant and is used as an anesthetic. v. Cannabis – found in the leaves and flowers of Cannabis sativa (bhang). It is used to manufacture some drugs. vi. Nicotine – found in leaves of tobacco plant and is used in the manufacture of insecticides and narcotic drugs. It also manufactures cigarettes. vii. Rubber – it is made from latex of rubber plant. It is used in shoe industry and manufacture of chewing gum. viii. Colchicines – it is used in plant breeding and treating of cancer. ix. Pappain- it is obtained from raw paw paw and it is used as a meat tenderizer. x. Khat/miraa – it’s chewed and acts as a mild stimulant. Excretion and Homeostasis in Unicellular Organisms  Most simple organisms such as the protozoa (amoeba and paramecium) live in aquatic environment.  They depend mainly on diffusion as the means of excretion.  Their bodies have a large surface area to volume ratio providing a large surface area for gaseous exchange and excretion to take place by simple diffusion.  Waste products diffuse from the cytoplasm where they are highly concentrated across the cell membrane into the surrounding water where their concentration is low.  The organisms also use the contractile vacuole to achieve excretion.  Amoeba and paramecium live in an aquatic environment that is hypotonic to their body fluids. Water therefore tends to move into their cytoplasm by osmosis.  The excess water and dissolved chemicals accumulate in the contractile vacuole which releases them to the surrounding water. Diagram Excretion in Mammals  Mammals have an elaborate excretory system since their bodies are complex. 44   The main excretory organs in mammals include; lungs, skin, kidneys and the liver. A Structure and Function of the Mammalian Skin  Skin is the largest body organ covering the whole body surface.  It has the following functions. i. Protection of the underlying tissues from entry of micro- organisms, physical damage and ultra violet rays from the sun. ii. Regulation of body temperature. iii. Excretion of salts, excess water and traces of urea. iv. Reception of stimuli such as heat, cold, pain, touch and pressure. v. Synthesis of vitamin D. vi. Storage of fats. Diagram  The skin is made up of two layers; a) Epidermis (upper and outer layer) b) The dermis (inner layer) a) Epidermis (upper and outer layer)  It is made up of three other layers; i. Cornfield layer. ii. Granular layer. iii. Malphigian layer. i. Cornifield layer  The Cornifield layer of the epidermis consist of dead cells which form a tough outer coat; that protects the skin against mechanical damage, bacterial infection and water loss; ii. Granular layer  It’s the middle layer of the epidermis and is made up of living cells that give rise to the Cornifield layer. iii. Malphigian layer  Malphigian layer consists of actively dividing cells that contain fine granules of melanin; that prevents the skin against ultraviolet light rays from the sun; melanin gives the skin its colour. b) The Dermis (inner layer) 45   It is thicker than the epidermis and consists of the following structures; 1) Sebaceous glands produce an oily secretion sebum which give hair its water repelling property; that keeps the epidermis supple and prevents it from dying Sebum also prevents bacterial attack due to its antiseptic property; 2) Has blood vessels; that dilate and contract; In hot conditions, they dilate; increasing blood flow near the skin surface enhancing blood flow near the skin surface; minimizing heat loss; Blood vessels supply nutrients and oxygen to skin tissues and also remove waste products and carbon IV oxide. 3) Has Hair follicle ;hairs stand during cold weather thus trapping a layer of air which prevents heat loss; In hot weather they lie close to the skin surface; to enhance heat loss to the atmosphere. 4) Have many sensory neurons which detects environmental changes; increasing sensitivity of the skins. 5) Has subcutaneous layer; contains fat which acts as a heat- insulating layer and a fuel storage. 6) Lymphatic vessels; they drain excess tissue fluid. 7) Sweat glands; are involved in temperature regulation through loss of excess heat by the evaporating water. Sweat also excretes excess water, mineral salts, urea and lactic acid. B The Lungs  They are involved with the removal of carbon VI oxide which is released by cells during their metabolism.  Carbon IV oxide would be toxic if it was left to accumulate in the tissues. C Structure and Function of the Kidney Diagram fig. 4.3; generalized urinary system of a mammal (page 88 KLB)  Mammals have a pair of kidneys which are bean shaped and dark red in colour. 46   The kidneys are surrounded by a layer of fat which cushions them against mechanical injury.  Above each kidney are the adrenal glands which secrete hormones.  Renal artery supplies blood to the kidneys and the renal vein removes the blood.  Ureter transports urine from the kidney to the bladder which temporarily stores the urine.  The mammalian kidney has three distinct regions; cortex, medulla and pelvis. Diagram fig. 4.4(a) and 4.4(b) (page 89 KLB) Cortex  It is the outermost region and is dark red in colour. Medulla  It is red in colour and extends to form conical structures called pyramids.  Pyramids open up into the pelvis. Pelvis  It’s white in colour and narrows down to form the Ureter.  The human kidney contains urinary tubules called the nephrons. Nephron  It is the basic functional unit of the kidney. Each nephron is made up two main parts;  Renal tubule  Glomerulus. Diagram fig. 4.6. The structure of the kidney nephron 47  X B A D C C The renal tubule has 5 main parts. 1. Bowman’s capsule 2. Proximal convoluted tubule 3. Loop of Henle 4. Distal convoluted tubule 5. Collecting tubule 1. Bowman’s capsule  It is a thin walled and cup shaped structure which contains the glomeruli.  Glomerulus is a fine network of blood capillaries enclosed by the Bowman’s capsule.  It is made the afferent and efferent arterioles.  Blood entering the kidney via the renal artery is rich in nitrogenous wastes such as urea.  Also it has dissolved food substances, plasma proteins, mineral ions, hormones and oxygen.  Afferent arteriole entering the Glomerulus is wider than the efferent arteriole leaving it.  This creates extremely high pressure in the Glomerulus coupled with the fact that renal artery branches directly from the aorta where blood is at high pressure. Diagram: structure of the nephron 48   Due to the high pressure in the glomeruli, the liquid part of the blood and dissolved substances of low molecular sizes including urea, glucose, salts and amino acids are forced out of the Glomerulus into the cavity of the Bowman’s capsule.  The large sized molecules in the plasma such as proteins and blood cells are not filtered out.  This is because the capillary walls of the Glomerulus and bow mans capsule have very small pores.  This process is known as ultra-filtration and the filtrate formed is called glomerular filtrate.  The filtrate then enters the proximal convoluted tubule. Diagram of ultra-filtration at the Glomerulus 2. Proximal convoluted tubule  As the filtrate flows along the renal tubules, most of the filtered substances in the glomerular filtrate useful to the body are selectively reabsorbed back into the blood.  The following substances are actively reabsorbed using energy in the proximal convoluted tubule; All glucose, Amino acids and Mineral salts.  The proximal convoluted tubule is adapted in the following ways for efficient re-absorption of these substances. i) Presence of mitochondria in the cells lining to provide with energy required ii) Cells of the tubule have micro-cilli (infoldings) which increase surface area for re-absorption. iii) Tubule is long and coiled to increase the surface area. iv) Coiling of the tubule reduces the speed of flow of filtrate giving more time for efficient re-absorption. v) Tubule is well supplied with blood capillaries. 3. Loop of Henle  This is where particularly sodium chloride is actively reabsorbed into the blood.  Loop of Henle has counter current flow between the flow of filtrate and the flow of blood i.e. the filtrate and blood flow in opposite directions. 49   The hormone Aldosterone secreted by the adrenal glands regulate the absorption of sodium salts.  Low content of sodium salts in the blood stimulates adrenal glands to secret more Aldosterone hormone and therefore more salts are reabsorbed from the filtrate. 4. Distal convoluted tubule  When the filtrate reaches here, some water is reabsorbed into the blood by osmosis.  This is made possible by the following; - Active intake of sodium salt into the blood at the loop of Henle increases the osmotic potential of the blood. - The antidiuretic hormone (ADH) secreted by the pituitary gland. ADH increases the permeability of the tubule and blood capillaries to water  When there is excess water in the body there is less production of ADH and less water is reabsorbed hence production of large amounts of dilute urine.  If the body has lost a lot of water such as through sweating, this raises the osmotic pressure of blood. Pituitary gland releases more ADH which increases permeability of the kidney tubules to water. More water is reabsorbed hence production of little but concentrated urine.  The distal convoluted tubule has large surface area, it is has a wall that is one cell thick and is surrounded by may blood capillaries. 5. Collecting tubule  The filtrate in the collecting tubule becomes the urine and moves to the collecting duct.  Urine flows into the pelvis via the pyramids and is finally emptied into the urinary bladder through the ureter. About 1-2 litres of urine are formed in a day.  About 250ml of urine in the urinary bladder initiates the urge to urinate. The sphincter muscles relax and urine pass. Urine Composition Substance % 50  Composition. Water 95% Urea 2% Uric acid 0.03% Creatine 0.1% Salts 1.4% Ammonia 0.04% Proteins 0% Glucose 0%  The quantity and concentration of the urine in animals is affected by i) Physiological adaptations. ii) Habitat of an organism e.g. terrestrial, desert or aquatic. iii) Structural adaptations of the animals e.g. a desert rat has long kidney tubules to increase water reabsorption. Study Questions. Page 93. Comparison Between Aquatic and Desert Animals Fresh Water Animals Desert Animals. i) Have many glomeruli to Few glomeruli to reduce increase ultrafiltration. ultrafiltration. ii) Short loop oh Henle to reduce Long kidney tubules to increase water reabsorption. water reabsorption. iii) Produce large quantity of Produce small quantity of dilute urine. concentrated urine. Comparison of Composition of urine with that of Glomerular Filtrate and Blood Plasma. Substance % Composition of; Plasma Glomerular urine Filtrate. Urea 0.03 0.03 2.0 Uric acid 0.005 0.005 0.03 Ammonia 0.001 0.001 0.004 Glucose 0.1 0.1 0 51  Amino acids 0.05 0.05 0 Mineral salts 0.70 0.70 1.4 Blood 8.00 0 0 proteins. Functions of the kidney include: i) Excretion. ii) Osmoregulation. iii) Ionic balance. iv) Regulation of PH Kidney Diseases i) Nephritis This is the inflammation of the glomerulus of the kidney. It is caused by bacteria or infections such as small pox and measles. Symptoms  Headaches and vomiting  Fever  Passing coloured urine  Presence of proteins in urine Treatment  Use of antibiotics ii) Use of just adequate amounts of salts and proteins in diets Kidney stones Causes  Lack of vitamins such as vitamin A and inadequate intake of water  Chemical salts in urine that crystallize to form hard stones. Symptoms  Increased frequency in passing out urine  Pain and soreness in the upper backside  Difficulty in passing out urine  Fever Control & Treatment  Seeking medical assistance 52   Taking a balanced diet with adequate amount of water and vitamins  Dialysis or artificial washing out of the wastes  Use of laser beam to disintegrate the stones  Kidney transplant iii) Kidney failure  This is the failure of the kidney to perform as a result of a drop in blood pressure due to heart failure, haemorrhage or shock.  If failure is due to other causes, the condition can be corrected by; - Kidney dialysis - Kidney transplant iv) Albiminuria (Proteins in Urine).  This is also called Proteinuria  Capillaries of the glomerulus lose their ability to be selective and start allowing blood proteins to pass through into the kidney tubules. These proteins are released in urine. D The Liver and its Structure  This is the second largest excretory organ after the skin. It receives blood from two blood vessels; the hepatic portal vein from the alimentary canal and hepatic artery from the aorta. Homeostatic Functions of the Liver 53  Regulation of blood sugar level  Excess glucose is converted to glycogen ;and stored in the liver under the influence of the hormone insulin secreted by the pancreas. Another hormone called glucagon; stimulates the conversion of glycogen to glucose; when there is shortage of glucose in the body; Glucagon is also secreted by the pancreas 1. Deamination  The liver breaks down excess amino acids; The amino group is removed as ammonia which is toxic;  Ammonia is changed into urea which is less toxic in the ornithine cycle. Ornithine Cycle 2NH3 + CO2 Enzyme arginase CO(NH2)2 + H20 Ammonia Carbon iv Urea Water (Toxic) Oxide (less toxic)  The remaining carbon skeleton oxidized to carbon IV oxide and water; this process leads to release of energy. The carbon skeleton may be converted to glucose to be used during respiration; 2. Detoxification  Toxic substances are made harmless in the liver e.g.  Ammonia from the process of deamination is converted in the liver into urea; which is less toxic.  Bacterial toxins are converted to less toxic substances by liver cells;  Hydrogen peroxide produced by respiring cells is broken down into water and oxygen which are harmless by the enzyme catalase found in the liver. Enzyme Catalase Hydrogen Peroxide Water + Oxygen 54  (H2O2) (H2O) (O2) 3. Regulation of plasma proteins  The liver produces most of the proteins found in blood; fibrinogen and prothrombin which play a role in blood clotting. Albumin and globulins are also produced by the liver. Globulins act as antibodies;. Albumin contributes to the maintenance of osmotic pressure in the body; Non essential amino acids are synthesized by the liver; 4. Storage of vitamins A, B,D,E and K and mineral salts  The liver store vitamins A, B, D, E and K. Iron released from the breakdownof erythrocytes is stored in the liver cells; in the form of a compound called ferritin. The liver therefore is a good source of these vitamins and iron; 5. Heat production (Thermoregulation)  The various metabolic activities of the liver lead to release of heat energy; This energy is distributed by the blood to other parts of the body hence contributing to maintenance of constant body temperature; 6. Inactivation of hormones and drugs  After performing their functions, hormones and drugs are chemically modified to inactive compounds; The by-products are eliminated through the kidneys and faeces and via bile; 7. Storage of blood  The large size and high capacity for contraction and expansion of its veins enables the liver to hold a large volume of blood; It therefore regulates the volume of blood in the general circulation depending on the body’s requirements ; 8. Regulation of cholesterol and fat metabolism  When carbohydrates are in short supply in the body, fats in different parts of the body are mobilized and taken to the liver; The fats are oxidized to carbon (IV) oxide and water with the production of energy or modified and sent to tissues for oxidation; 9. Manufacture of red blood cells in foetus. Liver Diseases and Disorders 55  1. Liver Cirrhosis  This is the hardening of the liver tissues due to death of liver cells.  This is caused by ingestion of toxic chemicals such as alcohol.  Bacteria, viruses and parasites such as liver flukes can also cause the disease. Control  Avoid excess alcohol.  Avoid fatty diets.  Low salt intake 2. Hepatitis  This is a viral disease causing inflammation of the liver.  It is transmitted through contaminated food, milk and water.  There are two types of hepatitis; Hepatitis A and B. 3. Jaundice  This is characterized by the yellowing of the skin due to the failure of the liver to excrete bile. Homeostasis  This is the maintenance of internal environment of cells under constant Conditions E.g. temperature, osmotic pressure, blood sugar and chemical constituents. Principles of Homeostasis  Various body systems such as circulatory, excretory, endocrine (hormonal) and nervous work in a coordinated way to bring about homeostasis.  These systems work on a feedback mechanisms. There are two types of feedback mechanisms. a) Negative Feedback Mechanism  When a factor in the body such as temperature or blood sugar level falls below normal or rises above the normal, it is detected and corrected via the negative feedback mechanism.  Such an action is through: 56  i) An increase in the level if it is dropping ii) A decrease in the level if it is increasing  This restores the condition to the normal. Further Excess Positive feed back Excess Corrective Mechanism (Negative Feedback) Normal Normal (Set (Set Point) Point) (Negative feedback) Corrective Deficiency Mechanism Positive feedback Further deficiency b) Positive Feedback Mechanism  In positive feedback mechanism, a change below or above the normal is not corrected. The following are some of the factors regulated through homeostasis. 57   Temperature  Osmoregulation (water and salt balance)  Ionic content regulation  Blood sugar regulation a) Temperature Regulation. (Thermoregulation)  Hypothalamus of the brain is the thermoregulatory center. It also controls other homeostatic processes such as Osmoregulation, and blood sugar level. Skin and Thermoregulation The skin is adapted in the following ways to effect thermoregulation; 1. It has Hair shaft;  Connected to erector pili muscles;  In low Temperature Erector pili muscle contract raising hair shaft erect;  Hair traps air which insulates the body/poor conductor of heat.;  In high temperature, the Erector pili muscle relax and extends;  Hair shaft lies on the skin;  Little or no air is trapped;  Skin loses heat through convection /conduction /radiation ; 1. Blood vessels  In High temperature they vasodilate;  More blood flows near skin surface;  Heat is lost through conduction /convection/ radiation;  In Low temperature they Vasoconstrict;  Little blood flows near the skin;  Less heat or ho heat lost through conduction/convection/ radiation; Diagrams 3) Sweat gland  In High temperature, Sweating occurs and ( evaporates) and Carries latent heat of vaporization; cooling the body; 4) Has subcutaneous layer; contains fat which acts as a heat- insulating layer. Organisms in cold areas have thick subcutaneous layer for heat insulation. 58 Homoiotherms and Poikilotherms Homoiotherms (Endotherms)  They are the animals whose body temperature is maintained at a constant body temperature despite the wide fluctuations in the temperature of the external environment e.g. birds and mammals. Poikilotherms (Ectotherms)  These are organisms with variable body temperature according to the temperature of the local atmosphere e.g. in organisms such as reptiles, amphibians, insects, and fish. Methods of Regulating Body Temperature in Animals. i) Metabolic activities of the Body, such as shivering to raise body temperature. ii) Insulatory mechanisms such as dilation or constriction of blood vessels, hair movement etc. iii) Behavioral activities such as clustering together, burrowing, basking, hibernation, aestivation, putting on warm clothes etc. iv) Presence of adaptive features such as hair/fur, subcutaneous tissue etc. Hibernation is where animals go into deep sleep for long period of time due to cold. Aestivation is where animals go into deep sleep due to dry and harsh conditions. Differences Between Homoiotherms and Poikilotherms. Poikilotherms Homoiotherms i) They are sluggish under i) They remain active even cold conditions. under cold conditions. ii) They hibernate to avoid ii) Only the small animals death by freezing under hibernate because they very cold conditions. have large surface area to volume ratio hence lose a lot of heat. iii) They aestivate under iii) They do not aestivate very hot conditions. because they can maintain constant body 59  temperature. iv) They are easy prey to iv) Not easy to prey because predators due to their they active always. hibernation and aestivation. v) Require less food v) Require more food because they get heat because they use it to from the environment to generate heat for warm their bodies. maintaining the temperature constant. b) Osmoregulation (Water and Salt Balance).  The osmotic pressure of the body fluids must be kept at a constant so as to have a favourable environment for the normal functioning of cells. This is determined by the relative amounts of water and solutes (salts) in the body fluids.  If the osmotic pressure of these fluids falls below that of the cells, the cells take in water by osmosis, swell and may burst.  If the osmotic pressure of thee fluids was higher than that of the cells, the cells would lose water and shrink.  The hypothalamus and the Pituitary gland are involved in Osmoregulation in the following ways; i) When the osmotic pressure of the blood rises due to dehydration, the hypothalamus is stimulated and sends an impulse to the pituitary gland which secretes the Antidiuretic Hormone (ADH) or Vasopressin into the blood. ADH increases permeability of the kidney tubules to water. More water is reabsorbed, osmotic pressure of the blood falls hence production of little but concentrated urine. ii) When osmotic pressure of the blood falls due to excess water in the body there is less production of ADH and less water is reabsorbed hence production of large amounts of dilute urine. Diabetes Insipidus  This is a condition whereby large quantities of dilute urine are produced when the pituitary gland fails to produce ADH or 60  produces it in inadequate amounts. This condition is also known as Diuresis. c) Regulation of Ionic Content  Important ions must be regulated within narrow ranges for efficient functioning of the cells.  Ions are involved in processes such as respiration, protein synthesis, muscle contraction etc.  The level of sodium ions is regulated by a hormone called Aldosterone produced by the adrenal glands.  When the level of sodium ions is low in the blood, more Aldosterone is released which stimulates reabsorption of sodium ions into the blood.  If sodium ions concentration in the blood rises above the optimum level, adrenal glands produce less Aldosterone into the blood and less amounts of sodium ions are reabsorbed. d) Regulation of Blood Sugar Level.  All sugars such as galactose, lactose and fructose are converted to glucose.  Glucose is broken down to release energy and excess is converted into glycogen and stored in the liver or converted into fats as stored as adipose tissue.  Some glucose flows in general circulation of blood and is maintained within a narrow range of 90-100mg per 100cm3 of blood.  The pancreas produces two hormones Insulin and Glucagon that are responsible for blood sugar regulation.  When there is excess sugar in the blood, insulin is produced and regulates the blood sugar level by the following; i) Converts excess glucose into glycogen for storage. ii) Inhibits conversion of glycogen to glucose. iii) Converts glucose into fats. iv) Increases breakdown of glucose to release energy.  When the level of the blood sugar falls, glucagon is secreted and corrects the situation by the following; i) Increases the breakdown of glycogen into glucose. 61 ii) Increases the conversion of fats and proteins into glucose. iii) Inhibits the conversion of glucose into energy. NB/. The hormone adrenaline produced by the adrenal glands also has homeostatic effect on glucose. It is released during emergencies to avail glucose for fight or flight. Diabetes Mellitus (Sugar Disease)  This is due to a deficiency in insulin secretion from the pancreas.  This leads to very high levels of sugar in the blood that cannot be utilised by cells hence eliminated by kidney in urine. Symptoms  Presence of glucose in urine  Loss of body weight due to breakdown of fats and proteins  Chronic starvation  Thirst sensation. Control  Insulin injection into the blood stream  Avoid foods rich in sugars.  Avoid excessive intake of alcohol. Question  Explain why insulin is not administered orally (through the mouth) 62  Corrective mechanism, the liver; i) Converts excess glucose into glycogen for storage. ii) Inhibits conversion of glycogen to glucose. iii) Converts glucose into fats. iv) Increases breakdown of glucose to release Rise energy. Fall Normal glucose Level. Normal glucose level 90mg/100ml blood 90mg/100ml blood Fall Corrective mechanism, the liver; Rise i) Increases the breakdown of glycogen into glucose. ii) Increases the conversion of fats and proteins into glucose. iii) Inhibits the conversion of glucose into energy. Revision questions Gaseous Exchange  This is the process by which respiratory gases (oxygen and carbon IV oxide) are passed across the respiratory surface.  Gases are exchanged depending on their concentration gradient.  In simple organisms such as amoeba, diffusion is enough to bring about gaseous exchange.  CO2 diffuses out into the surrounding water while oxygen diffuses from the water across the plasma membrane into the amoeba. Diagram 63 Importance of Gaseous Exchange 1. Promote oxygen intake for respiration. 2. Facilitate carbon IV oxide removal from the body as a metabolic waste product. Gaseous Exchange in Plants  During the day, green plants take in carbon IV for photosynthesis.  Oxygen is given out as a byproduct of photosynthesis and is released into the atmosphere. Examples of respiratory Surfaces in Plants  Stomata in leaves  Roots e.g. pneumatophores  Lenticels in woody stems Structure and Function of the Stomata  They are tiny openings on the leaf surfaces. They are made up of two guard cells.  Guard cells are the only epidermal cells containing chloroplasts. They regulate the opening and closing of the stomata. Adaptations of Guard Cells i) They are bean shaped/sausage shaped. ii) Contain chloroplast hence can photosynthesize. iii) Inner walls are thicker while outer wall is thin to facilitate the opening and closing of stomata. Diagram Mechanism of Opening and Closing of Stomata  There are three theories that try to explain how the stomata open and close. i) Photosynthetic theory ii) Starch Sugar inter-conversion Theory. (effect of changes in pH of guard cells) iii) Potassium Ion Theory. i) Photosynthetic theory  During the day, guard cells photosynthesize forming glucose.  This glucose increases the osmotic pressure in the guard cells.  Guard cells draw in water from the neighbouring epidermal cells and become turgid. 64   The stoma opens.  During the night, there is no photosynthesis due to absence of light.  Glucose is converted into starch lowering the osmotic pressure in the guard cells.  Guard cells lose water and become flaccid closing the stomata. ii) Starch Sugar inter-conversion Theory. (effect of changes in pH of guard cells)  This is under the influence of pH in the guard cells.  During the day CO2 is used up during photosynthesis raising the pH in the guard cells.  In this high pH, enzymes convert more starch into glucose.  Osmotic pressure of the guard cells increases and water enters into them, making them turgid hence opening the stomata.  During the night, there is no photosynthesis. The level of CO2 increases lowering the pH.  Enzymes become inactivated and starch is not converted into glucose.  Osmotic pressure of guard cells falls making them to lose water by osmosis.  Guard cells become flaccid and stoma closes. Mechanism of Gaseous Exchange in Plants  Oxygen diffuses from the atmosphere where it is more concentrated into the plant.  CO2 diffuses out as a metabolic waste product along a concentration gradient into the atmosphere. a) Gaseous Exchange through the Stomata  Stomata are modified in number of ways depending on the habitat of the plant. Xerophytes: These are plants adapted to life in dry areas.  They have less number of stomata that are small in size.  Stomata may be sunken, hairy and in some they open during the night and close during the day. Hydrophytes: These are the aquatic plants (water Plants) 65   They have many stomata that are large in size and mainly found on the upper leaf surface.  Hydrophytes have the aerenchyma tissue with large air spaces to store air for gaseous exchange. Diagrams Mesophytes: They are plants growing in areas with adequate amounts of water.  They have a fairly large number of stomata found on both leaf surfaces. b) Gaseous