Grade 11 Life Sciences Year Note 2023 PDF

A straight to the point note compiled in compliance with CAPS documents and the Life Sciences Examination guidelines. ISRAEL ADEYANJU LIFE SCIENCES YEAR NOTE GRADE 11 TABLE OF CONTENT 1. Important information 2023 3 2. Biodiversity and classification of Micro-organisms 4 3. Biodiversity of Plants 18 4. Biodiversity of Animals 35 5. Photosynthesis 40 6. Animal Nutrition (Human Nutrition) 44 7. Cellular Respiration 54 8. Gaseous Exchange 60 9. Excretion 74 10. Population Ecology 87 11. Human Impact 107 12. Reference 116 2 COMPILED BY ISRAEL ADEYANJU IMPORTANT INFORMATION 2023 A. FORMAT OF PROGRAMME OF ASSESSMENT (MPUMALANGA PROVINCE) Term Task Marks DATE 1 Practical Task 1 Min. 30 17 FEB. 2023 Controlled Test 1 100 10 MAR. 2023 2 Assignment 100 28 MAY. 2023 Controlled Test 2/June Exam 100/150 14 JUNE 2023 3 Practical Task 3 Min. 30 10 AUG. 2023 Controlled Test 3 100 22 SEPT. 2023 4 Final Examination (Paper 1 and 2) 300 NOVEMBER B. FORMAT OF LIFE SCIENCE EXAMINATION PAPER C. END OF THE YEAR EXAMINATION (NOVEMBER) 3 COMPILED BY ISRAEL ADEYANJU TOPIC 1: BIODIVERSITY AND CLASSIFICATION OF MICROORGANISMS (PAPER 2 – 29 MARKS) Living organisms are divided into five kingdoms: Living organisms Monera (bacteria) Protista Fungi Plantae Animalia All living organisms are classified into TWO groups (according to their cell structure): - Prokaryotes (Monera) - Eukaryotes (Protista, Fungi, Plantae, Animalia) Prokaryotes Eukaryotes Organisms without a true nucleus Organisms with a true nucleus DNA is not enclosed by a nuclear DNA is enclosed by a nuclear membrane and occurs freely in membrane inside the nucleus the cytoplasm Membrane-bound organelles are Membrane-bound organelles absent occur in the cytoplasm MICROORGANISMS - They are so small and cannot be seen with a naked eye. Can only be seen with the help of a microscope. - Several groups of microorganisms include viruses, bacteria, Protista, fungi. - Microorganisms are the most abundant organisms on earth and are found in huge numbers in every environment. - Most are harmless to plants and animals. - Some causes disease and are known as pathogens. - Most pathogens are parasites and live in or on other organisms - ALL viruses and SOME bacteria, protists and fungi are pathogenic in nature. VIRUSES - They are difficult to classify and are not placed under any of the five kingdoms. - Viruses have properties of both non-living particles as well as living organisms. - They are dormant (inactive) outside a living cell. However, they only reproduce inside cells of living organisms. - They are acellular (have no cell) and are therefore not classified as prokaryotes or eukaryotes. General characteristics - Viruses are parasites (organisms that lives on living cells or material and causes harm). - They are host – specific, while some are tissue – specific, e.g. poliovirus that only infects cells of nerve tissue. - They are pathogens and causes diseases in plants and animals e.g. TMV (tobacco mosaic virus in plants), AIDS, colds, flu, rabies, measles, polio etc. 4 COMPILED BY ISRAEL ADEYANJU - Viruses reproduce by converting the genetic material (DNA or RNA) of the host cells into viral nucleic acids so that new viruses can be produced. Basic Structure of Viruses - Viruses are very small (20nm – 450nm in diameter) and simple in composition. - They contain DNA or RNA (never both). - They are acellular and have no nucleus, cytoplasm or organelles. - Viruses can infect plant, animal or bacterial cells. A virus that infects bacterial cell is called a bacteriophage. - The shape of viruses varies from rod – shaped, spherical to more complex shapes. BACTERIA - The smallest and simplest living organism. - They occur in almost any imaginable habitat on earth. - Some live in the presence of oxygen (aerobic bacteria). - Others live in the absence of oxygen (anaerobic bacteria). - Some are pathogenic and cause diseases e.g. cholera, tuberculosis, anthrax. General characteristics - Bacteria are unicellular. - They have no true nucleus (prokaryotic). - Some are AUTOTROPHIC and produce their own organic substance (food) by photosynthesis or chemosynthesis. - Majority are HETEROTROPHIC and cannot produce their own organic substances. 5 COMPILED BY ISRAEL ADEYANJU Three types of heterotrophic bacteria are: - Parasitic bacteria (obtain food from living organisms). - Saprophytic bacteria (obtain food from dead organic material). - Mutualistic bacteria (obtain food from symbiotic relationship with another organism – both benefit in the relationship. Reproduction in bacteria occurs ASEXUALLY by binary fission, where a cell divides into two identical cells (same DNA). Basic Structure of Bacteria - Bacteria are unicellular and occur as single cells, filaments or colonies. - Bacterium cell is surrounded by a cell wall that consists of polysaccharides, proteins and lipids. - In some bacteria, the cell wall is surrounded by a slime layer or capsule, which protects the bacterial cell from desiccation and enemies. - A plasma or cell membrane which encloses the cytoplasm, occurs directly below the cell wall. - The cytoplasm has no membrane-bound organelles, such as vacuoles, plastids, mitochondria or ER, but ribosomes do occur. - True nucleus is absent. - Genetic material (DNA) is concentrated in a chromatin body (nucleoid). - Some bacteria move in liquid by means of flagella (singular: flagellum). Bacteria occur in various shapes: rod-shaped (bacillus/bacilli) spherical/round (coccus/cocci) Spiral-shaped (spirillum/spirilla) Comma-shaped (vibrio) 6 COMPILED BY ISRAEL ADEYANJU PROTISTS - They include mostly unicellular organisms that do not fit in any other kingdom. - It is the kingdom with the greatest diversity (with over 200 000 known species). - Protists are difficult to classify due to the large variety of organisms with different modes of nutrition, mechanisms of locomotion, cell coverings and life cycles. Protists are divided into three main groups: Protozoa – animal-like, unicellular, heterotrophic organisms e.g. amoeba, paramecium and plasmodium. Algae – plant-like, uni- or multicellular, autotrophic organisms e.g. macroscopic and multicellular red, brown and green algae, microscopic and unicellular diatoms, Euglena and dinoflagellates. Slime and water moulds – fungus-like, multicellular, heterotrophic organisms. General characteristics - All protists have true nuclei (eukaryotic). - Some are unicellular and microscopically small. 7 COMPILED BY ISRAEL ADEYANJU - Others are simple multicellular organisms that show a primitive level of cell differentiation and specialisation. - Algae are autotrophic while other protists are heterotrophic. - Reproduction is mostly asexual (binary fission). However, some algae do reproduce sexually. - Protists live in almost any environment where water occurs as most protists are aquatic. Basic Structure of Protists - Protists are uni- or multicellular. - Algae can photosynthesise because of presence of chloroplasts in their cells. - Various locomotory structures occur; pseudopodia (amoeba), cilia (paramecium), flagella (euglena and dinoflagellates). - Protozoa (animal-like) ingest their food by phagocytosis. - Cell wall composition varies in plant-like protists; green algae have cellulose cell wall, diatoms have cell walls of silica (shiny appearance). FUNGI They are divided into TWO main groups: - Macroscopic fungi e.g. mushrooms - Microscopic fungi e.g. yeasts (unicellular), thread-like moulds such as bread mould (multicellular) – some parts may be seen with the naked eye, but other parts are microscopic. General characteristics - Yeasts are unicellular, while mushrooms and moulds are multicellular. - All fungi have true nuclei (eukaryotic). - All fungi have cell walls made up of chitin. - All fungi consist of a mass of branched filaments or hyphae. - Fungi have no chlorophyll and are therefore heterotrophic. Most fungi are saprophytes (live off dead organic plant and animal matter, e.g. bread mould and mushrooms. Some are parasites (feed on living material), e.g. fungus that causes athlete’s foot. Some are mutualistic with other organisms (both organisms benefit) - Reproduction is, Unicellular fungi - asexually (binary fission). Multicellular fungi – asexually by spores (favourable condition), sexually by gametes (unfavourable condition). Basic Structure of Fungi (Structure of Rhizopus) - Rhizopus is multicellular and consists of a mass of branched filaments (HYPHAE). - The hyphae are interwoven to form the vegetative body, known as the mycelium. - Three types of hyphae can be distinguished: stolons, rhizoids, sporangiophore. - Rhizopus are thallus (no true roots, stems and leaves can be distinguished). 8 COMPILED BY ISRAEL ADEYANJU ROLE OF MICROORGANISMS IN MAINTAINING BALANCE IN THE ENVIRONMENT AND FOOD WEB - Role as producers in the food chain – autotrophic bacteria and algae (protists) produce their own organic nutrients. - Role as decomposers – decomposition bacteria, saprophytic fungi and protists (e.g. slime moulds) breakdown dead organic matter to their building blocks. In this way, elements like C, N, P, S are recycled in the environment and are made available for uptake by plants. - Role in the nitrogen cycle: Free-living bacteria and nodule bacteria convert free nitrogen into nitrates and make it accessible to plants. Nitrifying bacteria converts ammonia into nitrites and then nitrates which can be absorbed by plants. Denitrifying bacteria converts ammonia and nitrates into free nitrogen in the atmosphere. - Maintaining balance between Oxygen and Carbon dioxide – autotrophic bacteria and algae use carbon dioxide and release oxygen during photosynthesis. Algae is responsible for 50% of the Oxygen that is produced by photosynthesising organisms. 9 COMPILED BY ISRAEL ADEYANJU Role of microorganisms in symbiotic relationships Nitrogen-fixing bacteria – nodule bacteria absorb nitrogen from the air spaces between the soil particles and convert it into nitrates that the plant can absorb. In exchange, the nodule bacteria receive carbohydrates from the legume plant. Bacteria in the human intestine – Escherichia coli (E. coli) produce vitamin K, which plays an important role in blood clotting in humans. They also produce certain B vitamins. In exchange, E. coli bacteria obtain both nutrients from the human intestine as well as a protected habitat. DISEASES CAUSED BY MICROORGANISMS - HIV/AIDS - Tuberculosis (TB) - Malaria - Thrush (Candidiasis) HIV/AIDS Acquired Immune Deficiency Syndrome is a sexually transmitted disease caused by a virus (Human Immunodeficiency Virus). The virus infects cells of the human immune system (CD4 – cells). The virus reproduces (replicates itself) and destroys the CD4 – cells, which weakens the immune system, leaving the person more susceptible to other diseases. Effects on human body First phase shows few or no symptoms – flu symptoms (sore throat, headache, moderate fever, tiredness, muscle and joint pains, swelling of lymph glands and mouth ulcers) can occur. As the CD4 – count decreases further, more and more symptoms appear. These includes repeated cold sore infections, skin infections, prolonged fever, night sweats, chronic diarrhoea, opportunistic infections. Opportunistic infections are conditions that attack the body when the immune system is weak. Examples include respiratory infections, pneumonia, rare skin cancer, neurological conditions, lymph cancer, TB etc. The final phase of HIV infection is AIDS. Rare diseases and cancers become evident. The CD4 – count is very low. Death normally occurs as a result of the opportunistic infections. Effects on children, families and SA economy In an affected family, HIV can have an enormous impact on health, income, productivity and the ability to care for each other. If the breadwinner in the family becomes sick or dies, the family is left without income. When both parents die, the children become orphans (become the responsibility of their relatives or even government). AIDS affects people in their most productive years (20-40 years). Due to loss of young adults, the labour force is drastically reduced, and this has a negative impact on the SA economy (mining industry has a high rate of HIV infection). 10 COMPILED BY ISRAEL ADEYANJU Direct costs associated with HIV/AIDS include the cost of medical care and medication shouldered by the government. Indirect costs include time lost due to illness, recruitment and training costs to replace workers and costs for the care of AIDS orphans. Management of HIV/AIDS Testing – know your HIV status. Pre and post-counselling are vital. Treatment – currently there is no cure. - Antiretroviral drugs (ARVs) – decrease the viral load and give the immune system the chance to strengthen, but they cannot destroy the virus. - Healthy diet and vitamin and mineral supplements are important. - Treatment of common and opportunistic infections. Prevention – people must be well informed and educated. - Avoid sexual intercourse. - Have only one faithful, long-term, HIV-negative sexual partner. - Practice protected, safe sex (use a condom, even though it is not 100% safe). - Treat other STDs (syphilis, gonorrhoea etc.) - Avoid direct contact with blood (wear gloves, don’t share sharp objects) - Avoid alcohol and drug abuse – can lead to reckless sexual activity TUBERCULOSIS (TB) Infectious disease caused by Mycobacterium tuberculosis. It mainly affects the lungs but can also affect any other organ in the body. A person infected with the disease releases bacteria into the air by coughing, sneezing or spitting. The infected droplets may be inhaled, and the bacteria are thus transmitted to another person. TB is a poverty-related disease. In poor communities, people live together in over-crowded areas. Rooms lack light and ventilation, which increases the chances of infections. People’s resistance to the disease is further compromised by malnutrition and HIV/AIDS. Effects on human body When TB bacteria are inhaled, they reproduce and cause infection in the lungs. If the body’s immune system is strong, it will fight the infection and prevent the bacteria from spreading. If the immune system is weak, it may develop into active TB, where pneumonia occurs repeatedly and the bacteria spreads to other parts of the body. Symptoms of TB include: - Constant cough - Tiredness and fatigue - Loss of weight - Night sweats - Chest pain - Coughing up blood in saliva or mucus 11 COMPILED BY ISRAEL ADEYANJU Effects on family and community TB patients may lose months of income because he/she cannot work. If the breadwinner dies of TB, poverty increases in the extended family and dependents in the community. There is a stigma attached to TB. In certain communities, a man may leave his wife if she has TB. Untreated TB patients can infect family members and people in the community. Management of TB Treatment – involves aggressive course of antibiotics over 6 months. Prevention - People must be educated and well-informed about the spread of TB, the importance of hygienic conditions, sunlight, fresh air and a balanced diet. - Treatment of patients must begin directly after diagnosis to prevent the spread of TB. - Health care workers who work with TB patients must be well-informed about the risks of becoming infected. - Every baby must be vaccinated with the BCG vaccine against TB shortly after birth to provide immunity during childhood. Drug -resistant TB TB bacteria that are drug resistant do not respond to medication. The resistance is largely due to badly managed TB care and the incorrect use of anti-TB drugs. Multi-drug resistant TB requires long term chemotherapy involving very expensive medication and will only cure 50% of patients. These treatments are also very much more expensive than the treatment for normal TB. TB and HIV/AIDS TB is the most common opportunistic infection and cause of death for many HIV+ patients. If an HIV+ person develops active TB, the progression to the final stage of AIDS occurs much faster. TB and HIV/AIDS are a deadly combination, the one accelerates the other. MALARIA It is a parasitic disease caused by a protist of the genus Plasmodium and it is transmitted by the female Anopheles mosquito. When the mosquito bites an already infected person, a small quantity of blood is sucked up. This blood contains malaria parasites and they develop further inside the mosquito. When the mosquito bites the next person, the parasites are injected into the bloodstream via the mosquito’s saliva. The Anopheles female mosquito is the primary host as well as the vector (an organism that transmits a pathogen from one host to another) of the malaria parasite, while humans are the secondary hosts. 12 COMPILED BY ISRAEL ADEYANJU Effects of malaria The parasites move in the bloodstream to the liver after infection, where they multiply. The parasites then enter the blood, multiply within the red blood cells and cause the following symptoms: - Fever - Headache - Shivering - Joint pain - Vomiting - Convulsions Complications, such as brain damage, may also develop and cause a condition known as cerebral malaria. Malaria is associated with poverty but can also be a cause of poverty. Management of malaria - Treatment - Elimination of the vector mosquitoes - Use of mosquito nets treated with insecticides - Use of prophylactic medication to prevent the disease - Immunisation/vaccination IMMUNITY Immune response – the way in which an organism protects itself against pathogenic viruses, bacteria, protozoa or fungi. The immune system must be able to determine what belongs to the body, as opposed to what is foreign to the body. Immune response is divided into TWO main categories - Natural immunity – present at birth. - Acquired immunity – developed through exposure to pathogens. Natural immunity is the first line of defence against pathogens that infiltrate the body. It is not aimed at one specific type of pathogen, but able to destroy different pathogens. If the pathogen penetrates the first line of defence, the acquired immune response will be activated. Immune response in animals (Humans) Humans have both natural and acquired immunity. NATURAL IMMUNITY – external barrier that prevents harmful substances from entering the body. First line of defence - Skin - Coughing and sneezing reflexes 13 COMPILED BY ISRAEL ADEYANJU - Washing action of tears - Mucus secreted by the respiratory tracts (to trap microorganisms). Second line of defence Fever (increases body temperature) and inflammation (causes redness, pain, heat and swelling at the site of injury) which prevent the multiplication and spread of pathogens. ACQUIRED IMMUNITY – It may be classified in TWO ways according to the method in which immunity is obtained. Naturally acquired immunity – antibodies transferred from mother to foetus either through the placenta or mother’s milk (passive) OR direct contact with pathogens which stimulates the immune system to produce antibodies. Artificially acquired immunity – develops through deliberate action such as immunisation. In acquired immunity, pathogens that have penetrated the body tissues are actively destroyed and the body stores a memory of the response. ANTIGENS – protein molecules that occur as markers on the surface of all body cells, viruses, bacteria, protozoa and fungi. The white blood cells (leucocytes) recognise the pathogens as foreign cells as soon as they enter the bloodstream, due to the antigens on their cell surface. The pathogens are immediately destroyed or neutralised by the white blood cells. There are TWO types of leucocytes: - Lymphocytes (B- and T-lymphocytes) which occur in the lymph glands, spleen and blood. - Phagocytes are large white blood cells that can change shape and are produced in the red bone marrow. B – lymphocytes 14 COMPILED BY ISRAEL ADEYANJU T – lymphocytes Phagocytes Newly formed B-lymphocytes produce antibodies (1000’s per second) that are released into the blood plasma. The CD4-cells (T-helper cells) are another type of T-lymphocyte, which help other T- lymphocytes by initiating the immune response against infection. Some B- and T-lymphocytes become memory cells that remain in the blood. When the body is infected by the same pathogen, the memory B-lymphocytes will multiply and produce more 15 COMPILED BY ISRAEL ADEYANJU antibodies. The T-lymphocytes will also react faster if the body is re-infected with the same pathogen. The pathogen is killed before it can multiply and cause illness. It is the memory cells that remain in the blood, not the antibodies. The process by which phagocytes engulf pathogens is phagocytosis. IMMUNISATION AND VACCINE Immunisation (vaccination) – administration of vaccine orally (by mouth) or by means of injection to develop immunity to a disease. A vaccine is usually made up of dead or weakened form of the pathogen that causes the disease. The vaccine stimulates the body’s immune system to produce antibodies and also to develop a memory of the response. BIOTECHNOLOGY Biotechnology – the use of living organism (particularly microorganism) or biological systems in industrial processes. These include: Production of antibiotics – antibiotics are chemical substances that destroy only bacteria and not viruses e.g. Penicillin extracted from fungus Penicillum notatum. Production of insulin Production of food – some bacteria, yeasts and fungi are used in making foods such as bread, wine, beer, cheese etc. Antibiotics Chemical compositions of antibiotics differ. They work in different ways to destroy different bacteria. Some kill bacteria by destroying the structure of the bacterium e.g. cell wall, cell membrane. Others inhibit the metabolism of the bacterium e.g. no cell proteins and enzymes can be produced, which leads to the death of the cell. Bacteria may develop RESISTANCE to certain antibiotics through mutation. Reasons may be; - Incorrect antibiotic treatment – wrong antibiotic prescription, course of antibiotic is not completed, incorrect diagnosis (treating viral infection with antibiotics). - Unnecessary use of antibiotics. 16 COMPILED BY ISRAEL ADEYANJU Production of insulin 17 COMPILED BY ISRAEL ADEYANJU TOPIC 2: BIODIVERSITY OF PLANTS AND REPRODUCTION IN PLANTS (PAPER 2 – 29 MARKS) The Kingdom Plantae is divided into FOUR main groups or divisions: - BRYOPHYTES – mosses, liverworts and hornworts - PTERIDOPHYTES – ferns - GYMNOSPERMS – conifers, cycads, gnetales and ginkgo - ANGIOSPERMS – flowering plants Plants are divided into the four groups according to: 1. The presence or absence of: - Vascular tissue (xylem and phloem) - conducting tissues - True leaves, stems and roots - Spores or seeds - Fruits 2. The dependency on water for reproduction. Alternation of generation During the life cycles of each of the four plant groups two definitive generations occur: - Gametophyte generation – which is sexual and produces gametes - Sporophyte generation – which is asexual and produces spores. These two generations alternate in that the one generation gives rise to the other. This phenomenon is known as ALTERNATION OF GENERATION. 18 COMPILED BY ISRAEL ADEYANJU Dominant generation This refers to how often a plant uses the gametophyte or sporophyte stage in their life cycle. It is the generation that occupies the largest portion of the life cycle. - In BRYOPHYTES the dominant generation is the gametophyte generation. - In vascular plants (PTERIDOPHYTES, GYMNOSPERMS and ANGIOSPERMS), the dominant generation is the sporophyte generation. Advantage of a dominant sporophyte generation was fertilisation and dispersal of new/next generation timed with environmental conditions. Pollen grains in seed-bearing plants contain spores that when mature become the male gametophyte. BRYOPHYTES (e.g. mosses, liverworts, hornworts) The most primitive land (terrestrial) plants. They can only grow in moist and shady environments as they are dependent on water to complete the life cycle. Most mosses are able to withstand long periods of drying out and then seemingly spring back to life when water is available. 19 COMPILED BY ISRAEL ADEYANJU Characteristics 20 COMPILED BY ISRAEL ADEYANJU Life cycle PTERIDOPHYTES (e.g. fern plant) An intermediate group of plants between bryophytes (mosses) and seed plants. They occur in moist, shady environment. Ferns are more advanced in other respects in that they have vascular tissue and they are better adapted to living on land. Ferns can inhabit a wider range of habitats than mosses, but the water-dependent sexual generation of the life cycle is still a restriction on their distribution. 21 COMPILED BY ISRAEL ADEYANJU 22 COMPILED BY ISRAEL ADEYANJU Characteristics Life cycle 23 COMPILED BY ISRAEL ADEYANJU GYMNOSPERMS (e.g. pine tree) gymnos = naked; sperm = seed Examples are conifers (most abundant), cycads, gnetales and ginkgo Conifers Cycads Characteristics 24 COMPILED BY ISRAEL ADEYANJU Life cycle 25 COMPILED BY ISRAEL ADEYANJU ANGIOSPERMS The most advanced plants and most successful terrestrial plants e.g. mono- and dicotyledonous, Aloe and Petunia. Angiosperms provide food for humans in the form of cereals, fruit and vegetables. Characteristics 26 COMPILED BY ISRAEL ADEYANJU Life cycle Adaptations for a successful life on land Adaptation includes: - CUTICLE – to prevent water loss - STOMATA – for gaseous exchange - TRUE ROOTS, STEMS, LEAVES – for absorption of water and mineral salts, transport and photosynthesis - VASCULAR TISSUE (xylem and phloem) – for efficient transport in the plants - SUPPORTING AND STRENGTHENING TISSUE – to keep the plant upright. - SEEDS – ensure that unfavourable conditions can be overcome, and the embryo can have a chance of survival. The adaptations are absent in the gametophyte generation of the Bryophytes and Pteridophytes. The gametophytes are poorly adapted to life on land. The sporophyte generations of the two are better adapted but Pteridophytes are better suited to a terrestrial environment than that of Bryophytes. The sporophytes of Pteridophytes have 27 COMPILED BY ISRAEL ADEYANJU true roots, stems and leaves, vascular tissue, a cuticle, stomata and sporangia that require dry environment for spore dispersal. Bryophytes and Pteridophytes are both dependent on water for fertilisation. Gymnosperms and Angiosperms are a step above the Pteridophytes. They are not dependent on water for fertilisation and they also form seeds. Angiosperms are the best adapted of all the groups. They bear flowers, and the seeds are enclosed in fruits. 28 COMPILED BY ISRAEL ADEYANJU REPRODUCTION IN PLANTS TYPES OF REPRODUCTION Asexual reproduction – only one parent is involved, and ALL offspring have the same genetic composition as the parent. No gametes (sex cells) are involved. The process occurs by mitosis. Asexual reproduction is more common in plants than in animals. Advantages - In favourable conditions, a large number of offspring are produced rapidly and simply. - Energy expenditure is low, because no gametes are produced. - Offspring will easily adapt in the same environmental conditions as the parent because they are identical. Disadvantages - All the offspring share the same weak characteristics. If the stable environment changes, the consequences could be fatal and drastically reduce their chances of survival. - Too many offspring are usually produced. This leads to overpopulation. Competition for food and space increases. Sexual reproduction – two parents are involved, and their genetic materials combines. The offspring are not identical to each other, or to either of the parents. Gametes (sex cells) are produced by meiosis. Fertilisation takes place, during which the male gamete (sperm) and a female gamete (egg cell) fuse to form a zygote, which will develop into a new individual. Advantage - Offspring show greater genetic variation. They are more adaptable and have a greater chance of survival in changing environments. Disadvantages - The process takes longer than asexual reproduction. Gamete formation takes time. - Fewer offspring are produced, decreasing the chances of survival. - Energy expenditure is higher than in asexual reproduction. Special reproductive organs (flowers) develop. - Plants need agents (e.g. water, wind or insects) to disperse pollen and seeds. FLOWERS AS REPRODUCTIVE ORGANS Flowers are the reproductive organs of Angiosperms. Flower of a dicotyledonous plant, e.g. Petunia consists of four whorls (ring of floral parts): CALYX – the outermost whorl. It consists of five small, green sepals. The SEPALS surround the other whorls and protect the flower in the bud stage. COROLLA – it consists of five striking, brightly-coloured petals that are fused together to form a trumpet-shaped corolla. The PETALS attract insects and birds to the flower for pollination. ANDROECIUM – it composes the male part of the flower known as STAMENS. The Petunia has five stamens that are attached to the inside of the petals. Each stamen consists of a long 29 COMPILED BY ISRAEL ADEYANJU filament ending in a lobed ANTHER. The anther contains pollen sacs in which the pollen is formed. GYNOECIUM – it is the female part of the flower. It consists of a single STIGMA, a thin STYLE and an OVARY. The surface of the stigma is sticky so that the pollen grains can stick to it. The ovary contains two locules (small cavities) with a large number of ovules. Flower of monocotyledonous plant, e.g. Aloe consists of three whorls: PERIGONE – the calyx and corolla are fused to form a PERIGONE. The Aloe flower consists of six perigone leaves that are arranged in two whorls of three leaves each. The perigone performs the same function as the sepals (CALYX) and petals (COROLLA). ANDROECIUM – it consists of six stamens arranged in two whorls of three each. GYNOECIUM – it consists of stigma, style and ovary. The ovary has three lobes. 30 COMPILED BY ISRAEL ADEYANJU POLLINATION It is the transfer of ripe pollen from an anther to a receptive stigma so that fertilisation can occur. Two types of pollination can be distinguished: Self-pollination: Transfer of ripe pollen from an anther to a receptive stigma of the same flower or other flowers on the same plant. Cross pollination: Transfer of ripe pollen from the anther of one flower to the receptive stigma of a flower on another plant of the same species. How pollination takes place During pollination, a ripe pollen grain (male spore) lands on a receptive stigma. After pollination the pollen grain germinates and develops a pollen tube with two male gametes. The germinating pollen grain, containing the two male gametes, represents the male gametophyte. The pollen tube grows down the style into the ovary and penetrates the ovule and eventually the embryo sac to release the two male gametes. The embryo sac inside the ovule contains an ovum and two polar nuclei. 31 COMPILED BY ISRAEL ADEYANJU Adaptation of flowers for pollination Pollination occurs by means of various pollinators (agents that transfers pollen), e.g. - Wind - Insects - Birds - small mammals (mice or bats) - Water Pollination by wind A wind pollinated flower; - Has small, not easily noticeable flowers without any bright petals - Is simple – petals and sepals are usually absent for better exposure to the wind. - Produce no nectar. - Has its flowers carried in groups, close to each other, at the tips of long stems. - Has long thin filaments hanging out of the flowers and are easily shaken by the winds. - Has large anthers which release large quantities of pollen. - Has small and light pollen grains that are easily carried by the wind. - Has long and feather-like stigma with a large surface area. They are suspended outside the flower, easily trapping pollen. Pollination by insects An insect pollinated flower; - Is brightly coloured to attract insect - Has a sweet scent. - Produces nectar as food for insects. - Has a sticky pollen so that it can easily stick to the insect’s body. - Has stamens and stigma positioned inside the flower to ensure that the pollen on the insect’s body can rub off onto the sticky stigma while it searches for nectar. Pollination by birds A bird pollinated flower; - Is brightly coloured, often red, orange or yellow, to attract birds. - Produces large quantities of nectar to attract birds. - Has little or no smell – birds have a weak sense of smell. - Is trumpet-shaped, with stamens and stigma protruding from the flower. - Has flowers placed on the tips of long, solid, leafless stems that protrude above the plant leaves. This makes them accessible to birds in search of nectar. FORMING OF SEEDS Fertilisation occurs after pollination. - The fertilised ovule now develops into a seed that encloses and protects the embryo and endosperm (tissues in the embryo). - The tissue around the ovule hardens to form the seed coat (testa). 32 COMPILED BY ISRAEL ADEYANJU - The embryo develops into one or two cotyledons that store reserve food. - The ovary around the fertilised ovule develops into a fruit that protects the developing seed. The fruit either opens or is eaten to release the seeds. - Seeds are dispersed by the wind, water, insects or animals (including humans). - Germination occurs when the seed absorbs water. Importance of seeds - Seeds are adapted to be dispersed by winds, insects, animals, water or humans. Effective seed dispersal means that the new seedlings germinate far from the parent plant. In this way species are well distributed to reduce competition. - Seeds store reserve food in the endosperm for the early development of the embryo. Reserve food makes it possible for seeds to survive harsh weather conditions by remaining dormant. - The hard, resistant seed coat (testa) that surrounds the seed protects the embryo against unfavourable condition. - The cotyledons of the embryo provide food for the young developing seedlings after germination. 33 COMPILED BY ISRAEL ADEYANJU Seed as a source of food Plants with edible seeds are a major source of food for humans and animals. Edible seeds are divided into THREE categories, i.e. - GRAINS e.g. corn, wheat, rice and oats are an important source of the energy-rich carbohydrates (starch). - LEGUMES e.g. peas, beans and lentils are an important source of proteins. - NUTS e.g. almonds, cashews, chestnuts, macadamias, walnuts have a high protein content, and are also high in fibre, anti-oxidants and mono-unsaturated fatty acids. Mono-unsaturated fatty acids help to protect the body against coronary heart disease. Many seeds, such as sunflower, peanut, soya and flax are rich in oils and are used to manufacture plant oils. Use of seed banks to maintain biodiversity Large numbers of wild plants in nature are endangered, mainly because of the destruction of habitats and climate change. By storing the seeds of these endangered plants, their extinction may be prevented. If the seeds of these plants are stored in a seed bank, they will not die out. Seeds stored in seed banks can be used to: - Re-establish endangered or extinct plants. - Rehabilitate damaged or destroyed habitat. - Cultivate plants that are overexploited. - Cultivate new hybrids that are harder and more resistant to disease. - Conserve endemic species. The protection of plant diversity is essential for food security as well as ecological well-being. 34 COMPILED BY ISRAEL ADEYANJU TOPIC 3: BIODIVERSITY OF ANIMALS (PAPER 2 – 18 MARKS) Kingdom Animalia can be divided into two main groups: - Invertebrates – Animals without a vertebral column (backbone) - Vertebrates – Animals with a vertebral column The TWO groups can be further subdivided into phyla according to shared characteristics. There are approximately 30 phyla in the animal kingdom, but only SIX will be discussed. - Phylum Porifera e.g. sponges - Phylum Cnidaria e.g. jellyfish, corals, sea anemones, blue bottles - Phylum Platyhelminthes (flatworms) e.g. Planaria, bilharzia worm, tapeworm - Phylum Annelida e.g. earthworms, sea worms, leeches - Phylum Arthropoda e.g. insects, spiders, crustaceans, myriapoda. (All five are invertebrates) - Phylum Chordata (vertebrates) e.g. fish, amphibians, reptiles, birds, mammals. BODY PLANS Scientists use body plans to classify animals into groups (phyla). Animals with similar body plans are classified together in a phylum. The following FOUR common features of an animal’s body plan are important when an animal is classified. - Symmetry and cephalisation - Number of tissue layers that develop in the embryo - Presence and absence of coelom and a blood system - Number of openings in the digestive tract (alimentary canal). Symmetry and cephalisation Symmetry occurs when an animal can be cut into one or more planes to obtain two mirror images. Asymmetry – Animals that show no symmetry are asymmetrical. Example is the sponges. Radial Symmetry – A radially symmetrical animal can be cut in more than one vertical plane through its centre to obtain two mirror images. They have no right or left side. Animals with radial symmetry are usually sessile (sedentary and attached to a substrate) or free-flowing. The major disadvantage of radial symmetry is that locomotion is slow and inefficient. Bilateral symmetry – A bilaterally symmetrical animal can only be cut in one vertical plane through its centre to form two mirror images. It has a definitive dorsal (top) and ventral (bottom) side, a left and right side, an anterior and a posterior end. Bilateral symmetry usually goes together with the development of specialised, sensitive area, the head, at the anterior end of the body. This concentration of nerve cells at the anterior end 35 COMPILED BY ISRAEL ADEYANJU of the body is known as cephalisation. A central nervous system is formed. Locomotion is made possible by cephalisation. Tissue layers that develop in the embryo The developing animal embryo consists of a mass of cells that are arranged in the shape of a ball. Different tissue layers (known as germ layers) can be distinguished: - Ectoderm – outer germ layer - Endoderm – inner germ layer - Mesoderm – germ layer between ectoderm and endoderm According to the number of germ layers that occur in the developing embryo, animals are classified as: DIPLOBLASTIC – the embryo has two germ layers: an outer ectoderm and inner endoderm. These two cell layers are separated by a non-cellular, jelly layer, the mesoglea. TRIPLOBLASTIC – the embryo has three germ layers: an ectoderm, endoderm and a mesoderm between the ectoderm and endoderm. Animals that show radial symmetry only have two germ layers and are always diploblastic. Diploblastic animals have a tissue level of organisation and do not develop organs. All bilaterally symmetrical animals are triploblastic with three germ layers and an organ level of organisation. Triploblastic animals are more advanced and complex than diploblastic animals. 36 COMPILED BY ISRAEL ADEYANJU Coelom and blood system A coelom is an internal fluid-filled cavity that develops in the mesoderm of triploblastic animals. The coelom separates the digestive tract from the body wall. Diploblastic animals do not have a coelom. In triploblastic animals we distinguish between acoelomate, pseudocoelomate and coelomate animals. Acoelomate – has no cavity (coelom) in the mesoderm. Pseudocoelomate – has a coelom, but it is not seen as a ‘true’ coelom because it is not only surrounded by mesoderm tissue. Coelomate – has a true coelom (a cavity) in the mesoderm. Coelomate animals are more advanced than acoelomate. A blood system developed in most triploblastic animals for the transport of O2, CO2 and digested nutrients as well as an excretory system to transport waste products. When the blood is restricted to the blood vessel, it is known as a CLOSED BLOOD SYSTEM. But when the blood is not restricted to the blood to the blood vessel, it is known as an OPEN BLOOD SYSTEM. Biological importance of coelom - It separates the digestive tract and the body wall – ensuring that each function independently of the other. - A fluid-filled coelom can act as a hydrostatic skeleton. 37 COMPILED BY ISRAEL ADEYANJU - The presence of a coelom allows animals to reach a considerable size and become more complex by providing space for organs to develop. - Coelomic fluid serves as a transport medium for substances such as gases, nutrients and wastes. Digestive tract Simple acoelomate animals only have one opening to the outside through which ingestion as well as egestion occurs. New food can only be taken in once all food already ingested has been digested and the undigested remains are egested. Coelomate animals are more complex and have two openings: a mouth and an anus. This is known as THROUGH GUT (complete gut). Incomplete food does not mix with outgoing undigested remains. 38 COMPILED BY ISRAEL ADEYANJU ROLE OF INVERTEBRATES IN AGRICULTURE AND ECOSYSTEMS Pollination – Insects like honeybees and butterflies act as pollinators. Decomposition – Invertebrates like beetles, flies, earthworms breaks down dead plant and animal matter to simpler chemical substances which are released into the soil and made available to plants. Aerating the soil – Earthworms, ants and termites dig underground tunnels. This digging loosens the soil and traps more air between the soil particles, which makes it easier for water to infiltrate the soil. EVOLUTIONARY HISTORY OF ANIMALS 39 COMPILED BY ISRAEL ADEYANJU TOPIC 4: ENERGY TRANSFORMATION TO SUSTAIN LIFE (PAPER 1 – 31 MARKS) PHOTOSYNTHESIS Photosynthesis is the building up of carbohydrates (glucose) from carbon dioxide and water using radiant energy from the sun that is trapped by chlorophyll. Oxygen is released. Raw materials required for photosynthesis - Carbon dioxide from the atmosphere - Water from the soil - Radiant energy from the sun - Chlorophyll in the chloroplasts of green plants - Enzymes Products of photosynthesis - Glucose, which is stored in plant as starch - Oxygen, which is released into the atmosphere Equation for the process of photosynthesis: chlorophyll CO2 + H2O + Radiant energy Glucose + O2 Enzymes Process of photosynthesis Photosynthesis takes place in the chloroplasts of plant cell. 40 COMPILED BY ISRAEL ADEYANJU Two phases can be distinguished: LIGHT PHASE – this takes place in the presence of light (light dependent) DARK PHASE – this can take place in light or darkness (light independent) Light phase The light phase takes place in the grana (granum) of the chloroplasts. Radiant energy is absorbed by the chlorophyll molecules in the lamella. This radiant energy is transformed into chemical energy. The chemical energy is used for two processes: - Water molecules are split up into energy-rich hydrogen atoms (which are transferred to the dark phase) and oxygen atoms (which are released into the atmosphere as a gas). This process is known as photolysis. - The energy carrier ATP is formed, and it is used again in the dark phase. Dark phase (Calvin cycle) The dark phase takes place in the stroma of the chloroplasts. Carbon dioxide that is absorbed from the atmosphere combines with the energy-rich hydrogen atoms from the light phase using the energy that is released from ATP (formed in the light phase). Energy-rich carbohydrates (glucose) are formed. Excess glucose is converted to starch for storage. Importance of photosynthesis - It keeps the concentration of oxygen in the atmosphere and water constant. - It keeps the level of carbon dioxide in the atmosphere and water constant. - Photosynthesis provides food for heterotrophic organisms. - Photosynthesis makes chemical energy available for cell functioning during cellular respiration. 41 COMPILED BY ISRAEL ADEYANJU Factors that influence the rate of photosynthesis - Light intensity - Temperature - Carbon dioxide concentration Light intensity An increase in light intensity results in an increase in the rate of photosynthesis, but only to a maximum level. If the light intensity becomes too high, the stomata close and carbon dioxide then become a limiting factor. Temperature Plants photosynthesise optimally at 25ᶛC. Temperature that are too high or too low inhibit the rate of photosynthesis. At low temperatures, enzymes become inactive and at high temperatures, enzymes denature. At high temperatures, the stomata close to limit water loss and then carbon dioxide becomes a limiting factor once again. Carbon dioxide concentration A decrease in CO2 concentration leads to a decrease in the rate of photosynthesis. An increase in CO2 concentration leads to an increase in the rate of photosynthesis. 42 COMPILED BY ISRAEL ADEYANJU ROLE OF OPTIMUM LIGHT, TEMPERATURE AND CO2 ENRICHMENT IN A GREENHOUSE SYSTEM A greenhouse is a structure with a glass roof and walls where plants are cultivated. It becomes fairly warm inside a greenhouse, because the sun heats the air, plants, soil and other objects within the structure. The warm air is trapped in the greenhouse. The aim of a greenhouse is to provide optimal conditions of light, temperature and CO2 for maximum growth of the cultivated plants. - Optimum light intensity accelerates photosynthesis and stimulates the growth rate of the plants. - It must be possible to regulate the temperature of the air in the greenhouse to keep it at an optimum temperature for maximum growth of specific plant types. - CO2 enrichment can occur on large scale by pumping CO2 gas from tanks into the greenhouse. Also, addition of sodium bicarbonate and organic materials to the soil, will increase the CO2 levels. 43 COMPILED BY ISRAEL ADEYANJU TOPIC 5: ANIMAL NUTRITION (PAPER 1 – 31 MARKS) Animals are unable to produce their own organic food. All animals are heterotrophic organisms that are dependent on other organisms for their nutrients. Animals usually obtain their organic food in a complex, insoluble form. Before the animal tissues can use this food, it must first be broken down into simpler, soluble nutrients. Five main processes in nutrition INGESTION – the food is taken in and enters the alimentary canal. DIGESTION – food is exposed to mechanical and chemical processes that change solid, insoluble food to simpler, soluble substances. ABSORPTION – the end products of digestion are absorbed into the bloodstream. ASSIMILATION – the cells absorb the nutrients from the blood and use it to build new cell structures and compounds. EGESTION – the process through which undigested remains are removed from the body in the form of faeces. Necessity for food - Provides energy – most of the energy is provided through the ingestion of carbohydrates and fats. - Growth and repair of damaged tissues – this requires ingestion of proteins - Regulation of body processes (e.g. cellular respiration and excretion) – this requires ingestion of vitamins, water and mineral salts. MODES OF NUTRITION IN ANIMALS Herbivores – e.g. cattle, sheep, antelope and giraffes, feed on plant material. Large volumes of food are ingested, as plant material has a very low energy value. Herbivores’ teeth are adapted in the following ways: - Incisors are sharp to cut off plant material - Canines are often absent. - Premolars and molars are large and flat to grind plant material. 44 COMPILED BY ISRAEL ADEYANJU Carnivores – e.g. lions, cats and leopards feed on animal material (meat). They ingest less food than herbivores, as the proteins and fats in meat have a much higher energy value than plant material. Carnivores’ teeth are adapted in the following ways to hold and tear off pieces of meat: - Incisors have sharp ends to bite off food. - Canines are long and strong to pierce, kill and tear prey apart. - Premolars and molars have protrusions with sharp edges to cut off the food. Omnivores – e.g. baboons and pigs, live on both plant and animal material. The amount of food omnivores consume depends on the energy value of the food they eat. Omnivores’ teeth are very similar to those of carnivores, except that their molars do not have such prominent protrusions. Both baboons and pigs possess well-developed canines which are used mainly for self- defence and social display (baboons). HUMAN NUTRITION THE DIGESTIVE SYSTEM – The human digestive system consists of the alimentary canal and accessory organs. ALIMENTARY CANAL – a long tubular structure that extends throughout the body. It consists of the mouth and mouth cavity, pharynx, oesophagus, stomach, small intestine, large intestine and anus. 45 COMPILED BY ISRAEL ADEYANJU ACCESSORY ORGANS – it includes the tongue, salivary glands, pancreas, liver, gall bladder. Structure and functions of the alimentary canal MOUTH AND MOUTH CAVITY – it is the upper opening of the alimentary canal. The roof of the mouth cavity consists of a hard, ridged palate at the front and a soft palate at the back. The mouth cavity also contains the tongue and the teeth toward the front, as wells as salivary glands. Function - The mouth cavity receives the food and begins the process of mechanical digestion by breaking down larger particles of food into smaller particles and mixing it with saliva. PHARYNX – located at the back of the mouth cavity. It leads to two openings (oesophagus and trachea –wind pipe). During swallowing, the opening to the trachea is closed by a small leaf-shaped cartilage structure called epiglottis which prevents food from entering the trachea and choking a person. Function - The pharynx is a common passage for food and air from the mouth to the oesophagus and the trachea. OESOPHAGUS – a hollow, muscular tube that connects the pharynx to the stomach. It is located behind the trachea. Function - The muscle in the wall of the oesophagus are responsible for peristaltic movements, which push the food bolus forward. 46 COMPILED BY ISRAEL ADEYANJU STOMACH – it is a sickle-shaped, sac-like organ that is located just below the diaphragm. Functions - The muscular wall causes churning movements that assist with physical digestion and also ensure that the food is mixed with gastric juices. - The glands in the stomach wall secrete gastric juices for digestion. SMALL INTESTINE – long, muscular tube of approximately 5m to 6m in length. It consists of three parts which are duodenum, jejunum and ileum. Functions - The layer of muscles in the wall of the small intestine causes peristaltic movements, which moves the chime (semi-solid food) forward and ensures that it becomes thoroughly mixed with the digestive juices. - Glands in the duodenal wall (crypts of Lieberkuhn and Brunner glands) secrete digestive juices (intestinal juice), which play a role in digestion. - The small intestine has millions of villi to increase the surface area for the absorption of digested nutrients. LARGE INTESTINE – consists of three parts which are colon, caecum and rectum (which ends with an opening on the outside, the anus). Functions - The large intestine secretes large amounts of mucus to aid egestion. - Water and useful substances (certain vitamins and bile salts) are absorbed from the semi-solid waste in the colon. - Undigested waste (faeces) is stored temporarily in the colon before it is egested via the anus. 47 COMPILED BY ISRAEL ADEYANJU Structure and function of the accessory organs TONGUE – it is a muscular organ. The back of the tongue is attached to the mouth floor. Functions - It has taste buds and serve as a taste organ. - It helps with the chewing process by pressing food against the hard palate and between the teeth. - This ensures that chewed food is mixed with saliva. - It rolls the food into a bolus (ball) - It helps with the swallowing process as it pushes the food bolus towards the opening of the throat. TEETH – Humans have four types of teeth, each with four different functions. - Incisors – bite and cut off food - Canines – hold food in place and tear it off - Premolars – chew and grind the food - Molars – chew and grind the food The human dental formula is: 2. 1. 2. 3 2. 1. 2. 3 SALIVARY GLANDS – the salivary glands open into the mouth cavity. There are three pairs of salivary glands: - Parotid salivary glands (located below the ears) - Submandibular salivary glands (located in the lower jaw) - Sublingual salivary glands (located under the tongue) Function - They produce and secrete saliva via ducts that open into the mouth cavity. PANCREAS – a tongue-shaped gland located just below the stomach. The pancreas is both an exocrine and endocrine gland. It is composed of two types of cell: - Normal pancreatic cells - Islets of Langerhans Functions - Normal pancreatic cells secrete pancreatic juice with enzymes which play a role in digestion. 48 COMPILED BY ISRAEL ADEYANJU - The islets of Langerhans secrete two hormones (insulin and glucagon) which control the blood glucose levels in the body. LIVER – the largest gland in the body and is located just below the diaphragm. It consists of two lobes, a large right lobe and a smaller left lobe. Each lobe is made up of tiny lobules that in turn consist of liver cells. The liver cells produce bile that is transported away from the liver to the gall bladder for storage via the common hepatic duct. Function - The liver produces bile, which is stored in the gall bladder. - Glucose is converted into glycogen for storage in the liver. - Any excess glucose is converted into fat and stored. - Excess amino acids are broken down to form urea and glucose in the liver by a process called deamination. - The liver is a detoxifying organ that absorbs and neutralises certain toxins such as alcohol. - Vitamins A, D, E, K and B12 are stored in the liver. - The liver synthesises heparin which prevents blood clotting. GALL BLADDER – a muscular sac located between liver lobes. It contracts to release bile when it is stimulated. Function - The gall bladder stores and releases bile that is produced in the liver. Bile contains bile acid, which are critical for digestion and absorption of fats and fat-soluble vitamins in the small intestine. DIGESTION Complex, insoluble food particles are broken down by digestion into simple soluble nutrients. There are TWO types of digestion: - Mechanical or physical digestion - Chemical digestion MECHANICAL/PHYSICAL DIGESTION – it includes chewing process (mastication), bolus formation, churning movement and peristaltic movement. 49 COMPILED BY ISRAEL ADEYANJU CHEMICAL DIGESTION – breaking down o large, insoluble molecules in food into smaller, soluble molecules by the addition of water. The reaction is known as hydrolysis and it takes place with the help of enzymes. Role of water during digestion - Acts as lubricant and facilitates chewing and swallowing - Acts as solvent for digested food - Transports digested food - Medium in which digestive reactions occur - Reagent for hydrolysis. 50 COMPILED BY ISRAEL ADEYANJU ABSORPTION Digested food is absorbed into the bloodstream. Most absorption of digested food occur in the small intestine. The small intestine is structurally adapted for maximum absorption. The length of the small intestine ensures that food remains for long periods, allowing enough time for maximum absorption. There are millions of villi in the wall of the small intestine, which increase the absorption surface considerably. The soluble (dissolved) nutrients are mainly absorbed through the villi. Absorption Process Glucose, the end product of carbohydrate digestion, is actively absorbed, against the concentration gradient, into the blood capillaries of the villi. Amino acids, the end product of protein digestion, are also actively absorbed, against the concentration gradient, into the blood capillaries. Glycerol and fatty acids, the end products of lipid digestion, are absorbed by diffusion. Vitamins – fat soluble vitamins A, D, E and K are passively absorbed into the blood capillaries, while water soluble vitamins B and C are passively absorbed or aided by carrier molecules. Mineral salts are both passively and actively absorbed into the capillaries. Water is absorbed into the capillaries by osmosis. Large amounts of water, certain vitamins and mineral salts are also absorbed in the colon. HOMEOSTASIS Homeostasis is the tendency of living organisms to maintain a constant composition of their internal environment within narrow limits, irrespective of changes in the external environment. Internal environment – body fluid in which the cells are bathed. For cells to function optimally, these factors must be kept constant: - Glucose levels - Ion/salt concentration - Water content - Oxygen and carbon dioxide concentration - Body temperature - pH/acidity - Metabolic waste Hormonal control of glucose concentration in the blood Two hormones (insulin and glucagon), secreted by the islets of Langerhans in the pancreas, control the glucose concentration in the blood. When the blood sugar level is higher than normal, the beta (β-) cells of islets of Langerhans detect this increase and insulin is secreted into the blood. Insulin reduces the blood sugar level in two ways: 51 COMPILED BY ISRAEL ADEYANJU - It increases the rate at which glucose is absorbed by the cells (especially liver and muscle cells) - It stimulates the conversion of glucose into glycogen and fat in the liver and muscles The decrease in the glucose is detected by the beta cells of islets of Langerhans, which in turn, inhibits the secretion of insulin. When the blood sugar level is lower than normal, the alpha (α-) cells of islets of Langerhans detect this increase and glucagon is secreted into the blood. Glucagon increases the blood sugar level by stimulating the conversion of glycogen to glucose for release into the bloodstream. The increase in the glucose is detected by the alpha cells of islets of Langerhans, which in turn, inhibits the secretion of glucagon. Insulin and glucagon are antagonistic hormones as they have opposite effects in the body. Diabetes mellitus It is a metabolic disease characterised by high glucose levels in the blood. It is a chronic, incurable disease. It is as a result of the beta cells of islets of Langerhans not producing enough insulin or not producing at all or insulin is produced but the body cells cannot use it effectively. Diabetes may occur: - When the body’s immune system attacks and destroys its own beta cells. - As a result of obesity and a person being overweight. - As a result of inactivity. - Age. Treatment and management: - Daily insulin injection - Regular exercise - Maintaining normal body weight through a balanced diet. Balanced diet A balanced diet contains all the necessary nutrients in the correct quantities. It should include the following: - Energy foods such as carbohydrates and lipids (fats). - Building materials such as proteins. - Protective nutrients such as vitamins and minerals. Human nutritional requirements vary according to their age, gender and level of activity: - Growing children need more protein than adults. - Men need more food than women. - Active people need more energy food. - Pregnant women need more calcium. - Older people need less food. 52 COMPILED BY ISRAEL ADEYANJU Energy in food – the energy value in food is measured in the units kilojoules/kilocalories (1 kJ = 4,2 kcal). Nutritional supplement – enhances or adds to the amount of vitamins, minerals, proteins and fats in the diet. Supplements are usually taken for health, sports, beauty/anti-ageing. Malnutrition If a person does not follow a balanced diet, he/she will suffer from malnutrition which can lead to a variety of nutrition-related diseases/conditions. - Kwashiorkor – occurs due to a lack of protein in the diet. It often occurs in growing children. - Marasmus – results from a general lack of energy food (especially carbohydrates and fats). It occurs in children older than six months who are breastfeeding without additional food. - Anorexia nervosa – a psychological condition where the person refuses to eat, although food is available. - Obesity – occurs when a diet high in energy foods is followed over a long period of time. Energy intake exceeds energy consumption, leading to excessive fat deposits in the tissues and around the organs. Obesity can lead to the following life-threatening diseases/conditions like high blood pressure, high coronary heart disease, high cholesterol, diabetes, depression, cancer. - Food allergy – occurs when the body considers a substance in food harmful and develops a defence mechanism against it. 53 COMPILED BY ISRAEL ADEYANJU TOPIC 6: ENERGY TRANSFORMATION TO SUSTAIN LIFE 2 (PAPER 1 – 22 MARKS) CELLULAR RESPIRATION Cellular respiration is the breaking down of organic compounds (glucose) with the gradual release of energy that is stored in ATP molecules. Oxygen is required, and carbon dioxide and water are released as waste products. All living organisms are composed of cells. Cells constantly perform work and therefore require energy. Organisms use energy for the following life processes: - Growth - Cell division - Digestion - Movement - Transport of substances in the body - Active transport against a concentration gradient. Raw materials needed for cellular respiration - Glucose - Oxygen Products of cellular respiration - Carbon dioxide - Water - ATP (energy) – the energy is not always used straight away. It is temporarily stored in the energy carrier, ATP. Equation for the process of cellular respiration: enzymes Glucose + O2 CO2 + H2O + ATP Photosynthesis is an anabolic (building up) process, because energy-rich glucose is built up. Cellular respiration is a catabolic (break-down) process, because energy-rich glucose is broken down. Places where cellular respiration takes place The first phase takes place in the cytoplasm outside the mitochondrion, known as the cytosol. The second and third phases occur inside the mitochondrion. 54 COMPILED BY ISRAEL ADEYANJU Process of cellular respiration - Aerobic respiration (requires oxygen) - Anaerobic respiration (does not require oxygen) AEROBIC RESPIRATION – three stages can be distinguished: - Glycolysis - Kreb’s cycle - Oxidative phosphorylation Glycolysis Occurs in the cytosol just outside the mitochondrion. This phase requires no oxygen and is therefore an anaerobic phase. - Glucose (which consists of 6 carbon atoms) is broken down step by step. - Two molecules of pyruvic acid, with 3 carbon atoms each, are formed. - Energy-rich H-atoms as well as small amount of energy, is released and stored in ATP. - Coenzymes (hydrogen carriers) carry the energy-rich H-atoms to the third phase (oxidative phosphorylation). Kreb’s cycle Occurs inside the mitochondrion. This phase requires oxygen and is therefore an aerobic phase. - Pyruvic acid enters the mitochondrion. - A series of cyclic reactions takes place. - Energy-rich H-atoms and CO2 is released. 55 COMPILED BY ISRAEL ADEYANJU - Coenzymes act as hydrogen carriers that transmit the energy-rich H-atoms to the next phase. Oxidative phosphorylation It takes place in the cristae of the mitochondrion. This phase requires oxygen and is therefore an aerobic phase. - Energy-rich H-atoms from the Kreb’s cycle are carried to a hydrogen transfer system by coenzymes. - H-atoms are transferred from one hydrogen acceptor to the next. - Every time an H-atom is transferred from one acceptor to the next, energy is released. - This energy binds a phosphate (P) molecule with ADP to form ATP, which is the energy carrier in the cell. - Oxygen is the final hydrogen acceptor. Two hydrogen atoms combine with one oxygen atom to form a molecule of water (H2O). ANAEROBIC RESPIRATION – it takes place in the absence of oxygen. Glucose is only partially broken down and therefore less energy is released. 56 COMPILED BY ISRAEL ADEYANJU Anaerobic respiration in the muscles during exercise - During vigorous exercise, the muscles do not receive enough oxygen. - The muscle cells must therefore respire anaerobically. - Only glycolysis takes place. - Glucose is broken down - Pyruvic acid is formed - Only a small amount of energy is released - Pyruvic acid is converted into lactic acid, which is released in the muscle cells - This process is known as lactic acid fermentation. Lactic acid is a toxin that leads to muscle stiffness and muscle pain. Oxygen is needed to convert the lactic acid back to pyruvic acid. Moderate exercise with deep breathing is needed to get rid of muscle stiffness. If there is sufficient oxygen, aerobic respiration takes place and pyruvic acid enters the Kreb’s cycle. The oxygen needed to get rid of lactic acid which accumulates in the cells is called oxygen debt. Anaerobic respiration in plants (e.g. yeast) - Only glycolysis occurs - Glucose is broken down - Pyruvic acid is formed - Only a small amount of energy is released - Pyruvic acid is broken down further - Carbon dioxide is released - Alcohol (ethanol) is formed. - This process is known as alcoholic fermentation The role of anaerobic respiration in industry - Yeast cells and other fungi respire anaerobically and are used to produce alcoholic beverages, such as beer and wine. - Yeast cells are also used to cause bread to rise during the baking process. - Certain bacteria can be used to produce cheese, yoghurt and sour milk under anaerobic conditions in the presence of sugar (lactose). 57 COMPILED BY ISRAEL ADEYANJU Making beer Making wine 58 COMPILED BY ISRAEL ADEYANJU Making bread Making cheese Comparison between aerobic and anaerobic respiration Similarities - Glucose serves as raw material in both processes. - CO2 is released in both processes. - Energy is released in both processes. Differences 59 COMPILED BY ISRAEL ADEYANJU TOPIC 7: GASEOUS EXCHANGE (PAPER 1 – 31 MARKS) Breathing – the mechanical process whereby air moves in and out of the lungs. Gaseous exchange – the exchange of oxygen and carbon dioxide across a gaseous exchange surface. Cellular respiration – the gradual release of energy from organic compounds (glucose) in the presence of oxygen. Necessity for gaseous exchange - The main function of the respiratory system is to absorb oxygen from the atmosphere and make it available to the cells for respiration. - Carbon dioxide is released by the cells during respiration and must continually be removed through gaseous exchange. - The increased carbon dioxide concentration in the body can dangerously lower the pH of the body fluids. Requirements for an effective gaseous exchange system/surface The gaseous exchange surface; - must be large – to maximise gaseous exchange. - must be thin – for quick and easy diffusion. - should be moist – gases must be in solution in order to diffuse through a membrane. - must have a transport system – for efficient transport of gases. - must be well protected – it is very thin and fragile. Gaseous exchange occurs by diffusion. Diffusion is the movement of molecules from a high concentration to a low concentration until equilibrium is reached. 60 COMPILED BY ISRAEL ADEYANJU 61 COMPILED BY ISRAEL ADEYANJU HUMAN GASEOUS EXCHANGE Structure of the respiratory system The human respiratory system consists of the: - Air passages - Lungs - Respiratory muscles AIR PASSAGES The air passages transport air to and from the lungs and include the nasal passages, pharynx (throat), trachea (windpipe), bronchi and bronchioli. - Nasal cavities: two external nostrils lead to the nasal cavities that are separated by a septum. Small hairs in the nasal cavities filter larger particles from the inhaled air. Each nasal cavity is divided into three passages by three curved turbinate bones. - Pharynx (throat): the nasal cavities open into the pharynx. The pharynx leads to two openings; the opening known as the glottis – which leads to the trachea and the opening leading to the oesophagus (gullet). - Trachea (windpipe): It is a long, tubular structure located at the front of the oesophagus. The larynx (voice box) which houses the vocal cords, is located at the top of the trachea. The larynx is a triangular box made of cartilage. At the top of the larynx is the epiglottis, a thin, leaf-shaped structure made of cartilage. The epiglottis closes the opening to the trachea (glottis) during the swallowing process. This prevents food from entering the trachea and chocking the person. The wall of the trachea is reinforced and kept open by C-shaped cartilage rings. The openings of the C-shaped cartilage rings, covered by involuntary muscle tissue, face toward the back and press against the oesophagus. This allows the oesophagus to expand as food moves down through it. 62 COMPILED BY ISRAEL ADEYANJU - Bronchi and bronchiole: The trachea divides into a right and left bronchus that enter the right and left lung respectively. The bronchi are lined with a mucous membrane and are held open by O- shaped cartilage rings. Inside the lungs, the bronchi divide into smaller branches, lose their cartilage and form the bronchioles. Each bronchiole ends in an infundibulum which consists of groups of alveoli. NOTE: All air passages are lined with a mucous membrane of ciliated columnar epithelial cells. Adaptations of the air passages to their functions 63 COMPILED BY ISRAEL ADEYANJU LUNGS External structure - The two lungs are located in the chest and are surrounded and protected by 12 pairs of ribs. - The intercostal muscles are found between the ribs. - The right lungs consist of three lobes, while the left lung has two. - The lungs are spongy and elastic. - Each lung is surrounded by a double membrane, the pleura. - There is intrapleural fluid between the two pleural membranes that prevents friction that occurs when the lungs shrink or expand. - The lungs are conical and rest at the bottom on a dome-shaped muscle plate, the diaphragm. Internal structure - Inside the lungs the bronchi branch out, becoming smaller and forming bronchiole - As the bronchioli branch out into smaller bronchioli, they lose their cartilage support and end in infundibula (lung sacs), which consist of group of alveoli. - The walls of the alveoli are very thin and consist of a single layer of squamous epithelium. - The alveoli are surrounded by a network of capillaries. The walls of the capillaries consist of a single layer of squamous epithelium (endothelium). The pulmonary arteries enter the lungs and branch into smaller arterioles to form a network of capillaries around the walls of the alveoli. The capillaries unite again and form venules that flow together to form larger veins and finally the pulmonary veins, which then leave the lungs. 64 COMPILED BY ISRAEL ADEYANJU Adaptations of the lungs for their functions RESPIRATORY MUSCLES Different muscles play a role during breathing: - Diaphragm: In its relaxed state, the diaphragm is a dome-shaped muscle plate. This muscle plate separates the chest and abdomen to form an airtight thoracic cavity. - Intercostal muscles: The intercostal muscles are located between consecutive ribs and consist of two sets (i.e. external intercostal and internal intercostal muscles). Ventilation of the lungs The process is also known as the mechanism of breathing. The movement of air between the atmosphere and the lungs is caused by a difference in air pressure between the atmospheric air and the air in the thoracic cavity and lungs (alveoli). The movement of the respiratory muscles (diaphragm and intercostal muscles) changes the volume of the thoracic cavity, which causes the difference in pressure. Ventilation of the lungs takes place in two phases, i.e. - Inhalation – air moves from the environment into the lungs. - Exhalation – air moves from the lungs to the environment. INHALATION - The diaphragm contracts and become flatter. - The thoracic cavity enlarges from top to bottom. - The external intercostal muscles contract, causing the ribs to move upwards and outwards. - The thoracic cavity enlarges from side to side and from front to back - The abdominal muscles relax so that the abdominal cavity can accommodate the viscera (all the internal organs) being pushed down by the diaphragm. - The total volume of the thoracic cavity is increased. - The pressure in the thoracic cavity and lungs decrease. - The elastic lungs expand. - Since the atmospheric pressure is higher than the pressure in the thoracic cavity and lungs, oxygen-rich air flows into the lungs. 65 COMPILED BY ISRAEL ADEYANJU NOTE: Inhalation is an active process, because it is associated with contraction of the diaphragm and external intercostal muscles, which increases the volume of the thoracic cavity. EXHALATION - The diaphragm relaxes and returns to its original dome shape. - The thoracic cavity becomes smaller from top to bottom. - The external intercostal muscles relax, causing the ribs to move downward and inward. - The thoracic cavity reduces in size from side to side and from front to back - The total volume of the thoracic cavity is reduced. - The pressure in the thoracic cavity and lungs increase. - Since the pressure in the chest cavity and lungs is higher than the atmospheric pressure, carbon dioxide-rich air flows out of the lungs. NOTE: Inhalation is a passive process, because it is associated with relaxation of the diaphragm and external intercostal muscles, which decreases the volume of the thoracic cavity. Inhalation Exhalation What happens when you whistle, sneeze, cough or shout? - Exhalation is forced and becomes an active process. - The internal intercostal muscles contract, causing the ribs to move even further inward. - The abdominal muscles contract and the intestines are pushed up against the diaphragm, forcing it further upward. - The volume of the thoracic cavity is further reduced. - The pressure within the chest cavity is significantly increased. - Air is forced from the lungs, making whistling, sneezing, coughing or shouting possible. Gaseous exchange Gaseous exchange takes place in the alveoli as well as in the tissues, from where the gases are then transported to their destinations in different ways: - Gaseous exchange in the alveoli. - Gaseous exchange in the tissues. - Transport of gases in the blood. 66 COMPILED BY ISRAEL ADEYANJU Gaseous exchange in the alveoli Exchange of O2 - The inhaled air in the alveoli has a higher oxygen concentration than the blood in the surrounding blood capillaries. - A diffusion gradient is therefore created between the air in the alveoli and the blood in the capillaries. 67 COMPILED BY ISRAEL ADEYANJU - Oxygen dissolves in a thin layer of moisture that lines the alveoli and diffuses through the thin walls of the squamous epithelium of the alveoli and endothelial walls of the capillaries into the blood. Exchange of CO2 - The blood that reaches the alveoli from the tissues has a higher carbon dioxide concentration than the air in the alveoli. - A diffusion gradient is therefore created between the blood in the capillaries and the air in the alveoli. - Carbon dioxide diffuses from the blood in the capillaries through the endothelial walls of the capillaries and thin squamous epithelial walls of alveoli into the air in the alveoli. Gaseous exchange in the tissues Exchange of O2 - Oxygenated blood reaches the tissues. - The blood in the capillaries has a higher oxygen concentration than the cells of the tissues. - A diffusion gradient is therefore created between the blood in the capillaries and the cells. - The oxygen diffuses through the endothelial walls of the capillaries into the tissue fluid that surrounds the cells and into the cells. Exchange of CO2 - The cells have a higher carbon dioxide concentration than the blood in the capillaries. - A diffusion gradient is therefore created between the cells and the blood in the capillaries. - The carbon dioxide diffuses from the cells into the tissue fluid and then diffuses into the blood in the capillaries. 68 COMPILED BY ISRAEL ADEYANJU Transport of gases in the blood Transport of O2 Oxygen is transported in the blood in two ways: - Most of the oxygen that diffuses from the air in the alveoli to the blood in the capillaries combines with haemoglobin in the red blood cells to form oxyhaemoglobin. - A very small portion of the oxygen dissolves in the blood plasma. Oxygen is transported via the heart to all the tissues in these two ways. Transport of CO2 Carbon dioxide is transported in the blood in three ways: - Most of the carbon dioxide that diffuses from the cells into the blood in the capillaries combine with water to form carbonic acid, after which it dissociates and is transported as bicarbonate ions. - A portion combines with haemoglobin to form carbaminohaemoglobin. - The smallest potion of the carbon dioxide dissolves in the blood plasma. Carbon dioxide is transported via the heart to the lungs in these three ways. Composition of inhaled air vs exhaled air EFFECTS OF EXERCISE ON THE RATE AND DEPTH OF BREATHING During exercise, the body needs more oxygen so that respiration can occur faster and more energy can be released. As a result, carbon dioxide is released, and the body has to get rid of the excess carbon dioxide. In order to breathe in more oxygen-rich air and breathe out more carbon dioxide-rich air during exercise, there is an increase in the rate and depth of breathing. The heart rate also accelerates in order to increase the oxygen supply to the muscle tissues and the carbon dioxide removal from muscle tissues. 69 COMPILED BY ISRAEL ADEYANJU The respiratory centre in the medulla oblongata of the human brain controls the breathing rate. The cardiovascular centre is also located in the medulla oblongata and controls the heart rate. Lung capacity Lung capacity refers to the total volume of air that the lungs can accommodate. The human lung capacity is about 5 litres (5 000 cm3). - Amount of air that is breathed in and out during normal breathing – tidal volume - Additional air breathed in after normal inhalation – inspiratory reserve volume - Additional air breathed out after a normal exhalation – expiratory reserve volume - Tidal volume + inspiratory reserve volume + expiratory reserve volume = vital capacity of the lungs - After the full exhalation, there is still air in the lungs, this is known as the residual volume and is never exhaled. With each inhalation, fresh air mixes with the residual volume. During times of increased demand for oxygen (e.g. during exercise) the tidal volume increases by using the reserve air volume to get more fresh air into the lungs. The result is that the depth and rate of breathing increases. The depth of breathing can be determined before and after exercise, by measuring the tidal volume before and after exercise. HOMEOSTATIC CONTROL OF BREATHING Chemoreceptors in the wall of the aorta and at the base of the jugular arteries are very sensitive to changes in the carbon dioxide concentration in the blood. As soon as the CO2 concentration in the blood increases (e.g. after/during exercise), the chemoreceptors send nerve impulses to the respiratory and cardiovascular centres in the medulla oblongata of the brain. The respiratory centre in turn sends nerve impulses to the diaphragm and intercostal muscles to accelerate contraction and relaxation. The rate and depth of breathing thus increases and more CO2 – laden air is exhaled. 70 COMPILED BY ISRAEL ADEYANJU The cardiovascular centre sends nerve impulses to the heart muscle and arterioles. The heart rate increases, the arterioles constrict and the blood flows faster. CO 2 is transported to the lungs faster, where it can be exhaled. The CO2 concentration in the blood thus returns to normal. Effect of altitude on gaseous exchange With an increase in altitude (height above sea level), atmospheric pressure drops and so does the amount of oxygen. People living at a high altitude usually have more red blood cells to transport a maximum amount of oxygen efficiently. 71 COMPILED BY ISRAEL ADEYANJU If a person living at sea level goes to an area high above sea level for a while, his/her body will adapt after a few days or even weeks and produce more red blood cells. In this way the oxygen – carrying capacity of the blood is increased. NOTE: it is especially important for athletes living at the coast, which is a sea level (e.g. Cape Town) who plan to participate in a competition at a higher altitude (e.g. Mpumalanga), to arrive at the higher altitude in advance. This gives his/her body enough time to adjust or else he/she will tire quickly. His/her body has too few red blood cells to carry enough oxygen to the muscle tissues for respiration and consequent energy release. Respiratory diseases and abnormalities The Effect of smoking on gaseous exchange Cigarette smoking causes a variety of diseases (lung cancer, coronary heart disease, stroke, emphysema and chronic bronchitis). Three harmful toxins found in cigarette smoke are nicotine, tar and carbon monoxide. These toxins cause hardening of the arterial walls (atherosclerosis). It stimulates the secretion of adrenaline, which leads to an increase in heart rate and blood pressure, which in turn increases the risk of heart disease and stroke. The tar paralyses the tiny cilia in the air passages and hampers their functioning. The tar accumulates and can eventually result in lung cancer. 72 COMPILED BY ISRAEL ADEYANJU Smoking also causes the walls of the alveoli to tear and form holes. A condition known as emphysema could result. If a person stops smoking, the lungs can slowly start to function more efficiently, but the torn walls of the alveoli will not heal. Artificial respiration If a person stops breathing, artificial respiration is necessary. Artificial respiration can be applied with a machine known as a ventilator. The most common form of artificial respiration is mouth-to-mouth resuscitation, which is applied as follows: - Carefully remove any blockage from the person’s air passages. - Place two fingers under the chin and the other hand on the forehead and tilt the person’s head back. - Pinch the patient’s nose closed, breathe in and place your mouth over that of the patient. - Exhale until his/her chest rises. - Remove your mouth from his/her mouth and allow the chest to move down. - Give 12 breaths per minute. - Continue in this way until the person starts breathing by himself/herself. 73 COMPILED BY ISRAEL ADEYANJU TOPIC 8: EXCRETION (PAPER 1 – 31 MARKS) A large number of chemical reactions are continuously taking place in the body cells. The sum total of all the chemical reactions that occur in a cell is known as metabolism. During metabolism, waste products such as carbon dioxide, excess water, salts and nitrogenous wastes (e.g. urea, uric acid and creatinine) are formed. These waste products must be removed continuously because they will poison the cells and inhibit normal functioning if allowed to accumulate. There are three confusing terms to be noted and distinguished: Excretion – the removal of metabolic wastes from the body. Egestion – the removal of undigested substances – substances that are not products of metabolism and were never inside the cells. Secretion – the release of useful substances that are produced by cells for important functions e.g. digestive juices, hormones and milk. In humans, the metabolic waste products diffuse out the cells, via the tissue fluid that surrounds them, to the blood in the blood vessels. The waste products are transported in the blood to several excretory organs, which have the ability to remove these waste products from the bloodstream and release them out of the body. Different excretory organs LUNGS – excrete carbon dioxide, water vapour and heat. KIDNEYS and BLADDER – excrete urine. Urine consists of: - excess water - mineral salts - nitrogenous waste products (urea, uric acid and creatinine). LIVER – excretes urea and bile pigments. Urea is transported in the blood to the kidneys and is excreted in urine. Bile pigments pass into the small intestine and are excreted as bile salts in the faeces. SKIN – excretes sweat via the sweat glands. Sweat mainly consists of: - excess water - salts - small amount of urea Metabolic waste products and their origin - CO2 is formed as a product of cellular respiration. - Excess water is formed as a product of cellular respiration, as well as from the intake of fluids and food. - Urea is formed in the liver from deamination of excess amino acids. - Uric acid is the end product of metabolism of nucleic acids. - Creatinine is formed from creatinine phosphate in the cells. - Bile pigments are formed in the liver during the breakdown of haemoglobin. 74 COMPILED BY ISRAEL ADEYANJU URINARY SYSTEM IN HUMANS The urinary system consists of two kidneys, two ureters, the bladder and the urethra. Two types of blood vessels, namely the renal arteries and renal veins, are associated with the urinary system. The two kidneys occur in the abdominal cavity, on either side of the vertebral column, just below the diaphragm. The kidneys receive oxygenated blood, rich in metabolic waste products, from the renal arteries. Deoxygenated blood, purified of metabolic waste products, is transported away from the kidneys via the renal veins. - The ureter (a tube) extends from each kidney and opens separately into the bladder. - The bladder is a thin walled muscular sac in which urine is temporarily stored. - The urethra is a tube that transport urine from the bladder to the exterior (outside). At the base of the bladder, is a sphincter muscle which controls the flow of urine to the urethra. STRUCTURE OF THE KIDNEY External structure Dark red, bean-shaped organ with the concave side facing the vertebral column. The renal artery enters the kidney and the renal vein and ureter leave the kidney at an indentation called the hilum. Kidneys are enclosed by a layer of fat, which; - protects the kidneys against mechanical injuries, - insulates them, - keeps them in position. 75 COMPILED BY ISRAEL ADEYANJU Internal structure (macroscopic) The kidney is surrounded by a connective tissue membrane, the renal capsule, for protection. Directly under the renal capsule is a reddish-brown region (the cortex). The inner region of the kidney, the medulla, is lighter in colour and contains tubes which are arranged in groups (the renal pyramid). The apex of each pyramid is known as the renal papilla. The tubes in each renal papilla open into a common renal calyx (pl: calyces). The renal calyces open into the widened region of the ureter, known as the renal pelvis. Internal structure (microscopic) Each kidney is made up of about one million small structures known as nephrons. The nephrons are the structural and functional units of the kidney. - Structural units – the building blocks making up the kidney. - Functional units – independent units performing the functions of the kidney. 76 COMPILED BY ISRAEL ADEYANJU Structure of a nephron Each nephron is made up of two main parts: - Malpighian body - Renal tubule Malpighian body It occurs on one end of the nephron and is situated in the cortex. It consists of two parts: - Bowman’s capsule (double-walled and cup-shaped) - Glomerulus (a network of capillary blood vessels). These capillary blood vessels are lined with a single endothelial layer (squamous epithelium) with pores between the endothelial cells. The blood vessel that transports blood to the glomerulus is known as the afferent arteriole. The blood vessel that transports blood away from the glomerulus is known as the efferent arteriole. The inner wall of the Bowman’s capsule consists of specialised cells, the podocytes. The podocytes are cells with projections between which small openings, the filtration slits, occur. 77 COMPILED BY ISRAEL ADEYANJU Renal tubule Long convoluted (coiled) tubule that is situated partially in the cortex and partially in the medulla. It consists of three parts: - Proximal convoluted tubule (directly after the Bowman’s capsule and is situated in the cortex). The widest part of the renal tubule. - Loop of Henle (situated in the medulla). - Distal convoluted tubule (situated in the cortex). The proximal and distal convoluted tubule are both lined with a single layer of cuboidal epithelium. Distal convoluted tubule from opens into a collecting duct together with a number of distal convoluted tubules from other nephrons. A few collecting ducts converge and form the ducts of Bellini. The ducts of Bellini are the tubes forming the pyramids that open into the renal calyx of the renal pelvis.

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