Biology for Form II-IV Notes

8/12/2019 Biology for Form II-IV Notes

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Biology For Form II-iV(Notes)

NUTRITION: Is The process of digestion and absorption of foods and the bodys use it for growth and replacement of cells.

Plant Nutrition

(i)Photosynthesis 1. Photosynthesis: It is the process of making food by usingcarbon dioxide, water, with the helpof sunlight and chlorophyll by green plants.2. Photosynthesis required: Carbon dioxide(CO2), Water, Chlorophyll, Sunlight. Word Equation for photosynthesis: Carbon dioxide + water sunlight ----> glucose + oxygen.

chlorophyllChemical equation for photosynthesis: 6(CO2) + 6(H20) sunlight-----> C6H12O6 + 6(H2O) chlorophyll3. Factors affecting the rate of photosynthesis:1) Light intensity (The strength of light).

Graph of rate of photosynthesis against light intensity A) Between regions A and B, an increase in the brightness of light increasesthe rate of photosynthesis. B) This indicates that the speed at which photosynthesis is taking place islimited by the amount of light available. C) At higher light intensities (i.e. after point C) a further increase in lightintensity would not increase the rate of photosynthesis. D) This implies that the photosynthetic process is receiving the maximumamount of light it can make use of. E) Hence, an increase in light intensity will not increase the rate. 2) Temperature. Effect of temperature on the rate of photosynthesis A) At low temperature, photosynthesis is inactive. B) As the temperature increase, the rate of photosynthesis also increase. C) At optimum temperature, photosynthesis is in its most active state.


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D) Above optimum temperature, the rate of photosynthesis decreases. E) At extreme temperature, photosynthesis stops, because the enzymesinvolved in this process are denatured. NOTE:Since photosynthesis can be affected negatively by heat, enzymes must be involved. 3) Concentration of CO2. A) As there are more CO2, the faster the rate of photosynthesis. B) CO2 concentration cannot exceed 0.03%, because that is the amount ofCO2 in the air. C) It can only exceed 0.03% under experimental conditions. 4. Importance of photosynthesis: It reduces the amount of CO2 in the air which is the main cause of global warming. It produces oxygen to support other organisms for doing respiration. It produces food which is the source of energy of other organism and itself. 5. The leaf:

The External structure of Leaf

The internal structure of a leaf 6. The important features about leaves: The cells in the palisade layer are packed with chloroplasts which containlots of chlorophyll.

This is where the photosynthesis goes on. The palisade and spongy layers are full of air spaces to allow CO2 to reachthe palisade cells. The cells in the epidermis make wax which covers the leaf structures,especially the top surface. This is to prevent water loss. The lower surface is full of biddy little holes called stomata. They are there tolet CO2 in. They also allow water to escape - this is how the transpirationstream comes about. Xylem and phloem vessels cover the whole leaf like tiny "veins", to deliver water to every part of the leaf and then to take away the food produced by theleaf. 7. The stomata: Stomata closes automatically when supplies of water from the roots start todry up. The guard cells control this. When water is scarce, they become flaccid, andthey change shape, which closes the stomatal pores. This prevents any more water being lost, but also stops CO2 getting in, so thephotosynthesis stops as well.


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(ii)Plant Mineral Nutrition 1. Nitrogen: Plants need nitrogen to make proteins. They got nitrogen from thecompounds of nitrogen from the soil. 2. Magnesium:

Important for making chlorophyll. 3. Plants lacking of magnesium: They will have leaves not healthily green. 4. Nitrogen -------> proteins --------> new cells. 5. Nitrogen-containing ions + carbohydrates --------> amino acids -------->proteins. 6. Plants lacking of nitrogen: They will not grow properly.

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(2)Animal Nutrition

(i)Food 1. There are 7 types of food: Carbohydrates. Fats. Proteins. Minerals. Vitamins. Fibre or roughage . Water. 2. Carbohydrates can be divided into two: Starch (To test for starch, use iodine solution, the colour will change fromorange to blue-black if starch is present). Glucose(To test for glucose, use benedict's reagent, the colour of the reagent will change if glucose is present). 3. Proteins: To test for the presence of proteins, use biuret's reagent. If the colour of thereagent changes to violet, it means that proteins are present. 4. Fats: Its presence can be tested by using the filter paper experiment or the alcoholtest. A grease spot can be seen if fats are present using the filter paperexperiment. 5. Minerals:


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They are the inorganic salts which do not provide energy but areindispensable to bodily functions. Examples of minerals are calcium, phosphorus, sodium, chlorine, potassiumand iron. 6. Vitamins:

They are not energy -providing food nor are they body-building food. They are for maintaining normal health and development. Lack of vitamins can cause diseases such as scurvy and rickets. 7. Fibre or roughage: They are the indigestible fibrous materials, e.g. cellulose, present in the diet. It provides bulk to the intestinal contents and helps peristalsis. Insufficient of fibre can cause constipation. 8. Water: They are the essential constituent of protoplasm. Insufficient of fibre can cause constipation. 9. A balanced diet is a type of diet which consists of all types of food at thecorrect amount. 10.Factors affecting the diet of individuals: Activity. Age. Sex. Body size. 11. Malnutrition (Unbalanced diet): Obesity- extremely overweight. Constipation - difficulty to remove faeces. 12. Carbohydrates and fats are the main source of energy. While proteins areused for growth i.e. to make new cells and repairing damaged tissues. 13. Carbohydrates are from glucose and starch. Fats are from fatty acids andglycerol. Proteins are from amino acids. Cholesterol is a kind of sterol which is essential for the formation cellmembrane.14.Vitamin C maintains healthy skin, gum and the lining of blood vessels. Lackof Vitamin C can cause scurvy. Vitamin C helps our cells to stick together. 15. Vitamin D helps the absorption of calcium. Lack of Vitamin D can causerickets. 16. Calcium is a type of mineral, it has the function:1) For strong bones and teeth. 2) Clotting of blood. 17. Lack of calcium can cause rickets. 18. Iron is also a type of mineral, it has the function of making haemoglobin inred blood cells. 19. Lack of red blood cells can cause anaemia.20. Stages of nutrition:


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1) Ingestion. 2) Digestion. 3) Absorption. 4) Assimilation. 5) Egestion. (ii) Digestion and the digestive system 1. Digestion is the process of breaking down food into its simplest form. This isnecessary so that food substances are small enough to be carried by the bloodand able to pass into the cells. 2. Mouth: Chews food up into easy -to-swallow balls. 3. Salivary glands: Produce an enzyme called amylase to start the breakdown of starch. Saliva contains mucous (sticky, slippery substance). 4. Oesophagus (Gullet): The food chutes from the mouth to the stomach. 5. Stomach: It pummels food with its muscular walls. It produces pepsin (an enzyme for digesting proteins) and renin (an enzymefor digesting milk proteins), they are also called the protease enzyme. It produces hydrochloric acid for three reasons: 1) To kill bacteria. 2) To give the right pH for pepsin and renin to work (pH2-acidic). 3) To neutralise the alkaline effect of saliva. Hydrochloric acid, pepsin and renin are called the gastric juice. 6. Small intestine: Duodenum: 1) Secretion of pancreatic juice which consists of the pancreaticamylase, trypsin (protease), lipase and bile. 2) Bile are emulsifying agent created in the liver, stored in the gall bladder andtransferred to the duodenum through the bile duct to emulsify fats. 3) Sodium bicarbonate are secreted into the duodenum to neutralise the acidiceffect of hydrochloric acid. Ileum: 1) Secretion of intestinal juice which consists of the intestinal amylase,maltase, lipase and protease. 2) It is where the foods are completely digested into its simplest form. 3) Carbohydrates are digested into glucose, proteins are digested into aminoacids, and fats are digested into glycerol and fatty acids. 4) This is also where the "food" is absorbed into the blood. 5) It is long and folded to increase surface area. Tiny finger-like things called villi cover the inner surface to increase the surface area for absorption. 7. Large intestine:


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Colon: 1) Excess water is absorbed from the food. Rectum: 1) To store faeces. 8. Anus:

The faeces (the indigestible food) are expelled.

A) Tongue. B) Salivary gland. C) Buccal cavity D) Oesophagus/gullet. E) Stomach. F) Duodenum.G) Ileum. H) Small intestine.I) Colon; Ascending colon. Transverse colon. Descending colon. J) Rectum. K) Large intestine.L) Anus. M) Gall bladder. N) Liver. O) Pancreas. (iii)Absorption. 1. Absorption is the process by which digested food are transferred into the blood stream through the villi of the ileum. 2. The capillaries of the villi will join up to form the hepatic portal vein whichcarries blood to the liver. 3. Glucose & amino acids will be sent to parts of the body that need them. 4. Excess glucose will be converted by the liver into a storage substance calledglycogen & stored in the liver. 5. Glycogen can be converted back to glucose when the body needs moreglucose. 6. Any more excess glucose will be converted to fats and stored in the adiposetissues under the skin. 7. Excess amino acids will undergo a process called deamination which is done by the liver.


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8. Deamination is the process by which amino acids are broken down intoglucose and urea. Urea is a nitrogenous substance which is sent to the kidneysfor disposal. 9. Another function of the liver is the breakdown of alcohol: Alcohol ----->carbon dioxide + water + energy. 10. Too much alcohol in the body can make the person unconscious.(iv)Assimilation. 1. Assimilation is the process by which some of the absorbed food materialsare converted into new protoplasm or used to provide energy. 2. Uses of glucose and fats: For energy (to respire). Making new cells. Repair & replace damaged tissues. Production of other proteins such as enzymes and hormones. Fats are used to form part of a cell such as the cell membrane and the nuclearmembrane. Fats are used as insulators.

TRANSPORT OF MATERIALS IN LIVING THINGS 1. Transport in plants

(i)Water and ion uptake. 1. Ion is taken up into the plants by: Osmosis. Active transport. 2. Water is taken up into the plants by: Root pressure. Transpiration pull. (ii) Transpiration and translocation. 1. Transpiration is the process by which water is lost from the leaves of theplants. 2. Factors affecting the rate of transpiration: Humidity. Temperature. Wind. Light. 3. Light: The rate of transpiration will be high when there is light. 4. Temperature: The higher the temperature, the higher therate of transpiration. 5. Humidity & wind:


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The lower the humidity, the higher the rate of transpiration. The wind blows away the water vapour surrounding the leaves, in other words, the humidity surrounding the leaves become low, so the rate oftranspiration is high. 6. Higher rate of transpiration when it is:

Windy. Hot. Less humid. Daylight. 7. How to measure the rate of transpiration: Using a potometer. 8. Translocation is the process by which food substances(glucose) aretransported to other parts of the plant through the phloem. 9. The foods are transported to other parts of the plant because: For energy. To make new cells.

2. Transport in humans

(i) The Heart.

The structure of the heart.

NOTE: The thickest part of the cardiac muscle indicates that it is the left partof the heart. 1. Functions of valves: To allow the blood to flow in one direction only. To prevent the backflow of blood. 2. The Double circulation:

a) Pulmonary and (b) systemic circuit.

3. The blood which carries oxygen is called oxygenated blood (from lungs to body). The blood which doesn't carry oxygen is called deoxygenated blood(from body to lungs). 4. The left side of the heart is more muscular and thicker because it pumps blood to all parts of the body. (ii) The Blood Vessels. 1. There are three types of blood: Arteries.


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Veins. Capillaries. (smallest) 2. Differences between arteries and veins: 1) Arteries have smaller central cavity than veins. 2) Arteries have thicker elastic and muscular wall than veins. 3) Veins have valves while arteries don't have valves. 4) The blood flows slower, smoother and at low pressure than arteries. 5) All arteries carry oxygenated blood except pulmonary artery while all veinscarry deoxygenated blood except pulmonary veins. 6) Arteries carry blood away from the heart to the body while veins carry bloodto the heart from the body. 7) The blood carried by arteries are bright red in colour while the blood carried by veins are dark red in colour. 8) Blood in arteries flow due to the pumping action of the heart while veinsflow due to the contraction of the heart. NOTE:Veins are big, slow and evil.(iii) The Blood. 1. Components of the blood: Plasma. Blood cells. Platelets. 2. Plasma is the liquid part of the blood, it contains: Blood cells. Platelets. Water. Blood proteins. Waste products. Hormones. Food substances; glucose, proteins, vitamins, etc. 3. The blood cells consist of two parts: Red blood cells. White blood cells. 4. Red blood cells are also known as erythrocytes which have the function oftransporting oxygen. 5. White blood cells are also known as leucocytes which have the function as adefense mechanism. 6. Platelets which are also known as thrombocytes have the function to clot blood. (involving the use of fibrinogen) 7. Fibrinogen work together with platelets to form fibrin. 8. Factors that may cause heart diseases: 1) Smoking. 2) Stress.


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3) Malnutrition i.e. obesity. 4) Lack of physical exercise.

GASEOUS EXCHANGE AND RESPIRATION 2. Respiration

(i) Respiration. 1. Respiration is the process of breaking down food to release energy in thepresence of oxygen. 2. There are two types of respiration: i) Aerobic respiration. ii) Anaerobic respiration. 3. Aerobic respiration is the process of breaking down food in living cells torelease a large amount of energy in the presence of oxygen. 4. Anaerobic respiration is the process of breaking down food in living cells torelease a small amount of energy in the absence of oxygen. 5. Aerobic respiration: Glucose + oxygen -------> 'E' + carbon dioxide + water C6H12O6 + 6O2 -------> 6CO2 + 6H2O + 'E' 6. Anaerobic respiration: Glucose --------> 'e' + ethanol(alcohol) + carbon dioxide (Microorganism andplants) Glucose --------> 'e' + lactic acid (Humans) (ii)Human Respiratory System. 1. Breathing is a mechanical process that involves taking in air into the lungs &takes out air from the lungs.

2. Inspired and expired air: Substance Inspired air Expired air 1. Nitrogen 2. Oxygen 3. Carbon dioxide 4. Noble gases 5. Water vapour 78% 21% 0.03% 1% Varies 78% 16% 4.5% 1%


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Saturated

3. Temperature of: 1) Inspired air is lower than body temperature. 2) Expired air is about the same as body temperature. (iii)Human Gaseous Exchange. 1. The respiratory system consists of: Lungs. Nose. Mouth. Trachea. Bronchi (bronchus sg.) Bronchioles. Alveoli (alveolus sg.) 2. The gas exchange system in man:

The gas exchange system in man (left lung cut open to show alveoli)

3. Inspiration & Expiration:

(a) Inspiration and (b) expiration.

A) Inspiration is an active process involving the contraction of: The external intercostal muscles; and The diaphragm muscles. B) Contraction of the external intercostal muscles pulls the rib cage upwardsand outwards, while contraction of the diaphragm muscles result in theflattening of the diaphragm. C) The net result is an increase in the volume of the thorax (the part of the body between the neck and the abdomen where the heart and lungs lie). D) Pressure in the thorax is thus reduced. E) Air is then sucked into the lungs, inflating the alveoli until the internalpressure equals that of the atmosphere. F) Expiration is a passive process. G) During expiration, only the internal intercostal muscles contract. The ribcage drops, mainly due to its own weight. H) The diaphragm relaxes and is forced into a dome shape by the falling ribcage. I) The volume of the thorax is decreased. J) Pressure is then exerted on the air in the lungs, forcing it out.


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seed bearing plants. They have vascular tissues. They are woody plantsmajority being evergreen trees. Few varieties are shrubs.General and distinctive features of the Division Coniferophyta

General characteristics 1. They have secondary growth whose thickening can be observed in crosssection of a stem revealing annual rings. Secondary Growth is the result ofgrowth Lateral Meristems (Vascular Cambium & Cork Cambium). 2. Most of the members of Coniferophyta live in cool climates where theyform evergreen forests. They keep their leaves year-round. 3. They have a large amount of internodal elongation which allows them togrow faster than the other higher plants. 4. They are Xeromorphic, a characteristic that help to protect them fromexcessive loss of water and therefore adapt survival in extreme habitats. 5. Most are large trees while a few are shrubs and other small plants. 6. Most of them have hard barks which protect inner softwood. Distinctive characteristics 1. Conifers are non-flowering but seed producing plants. 2. They have seeds born in cones shaped structures rather than in fruits. 3. They are gymnosperms which mean naked-seed plants because theyproduce seeds in cones rather than inside an embryo. 4. The leaves are needle-shaped and have a thick cuticle for protection andto decrease water loss.

The structure of Pinus The structure of a pine tree Pines are evergreen, coniferous resinous trees growing 380 m tall.The bark of most pines is thick and scaly. They have needle like leaves. Pinesare among the most well- known coniferous trees in the world. They thrive intemperate mountainous regions, but can also survive in tropical spots in thenorthern hemisphere. Pines live relatively long time than other coniferousplants. They may live between 100 and 1,000 years.

The Stem The bark of most pines is thick and scaly, but some species have thin, flaking bark. The branches are produced in regular whorls appearing like a ring of branches arising from the same point.

Leaves A cross-section of pine stem has several concentric rings with distinct borders between each ring. The center of the stem is called pith. These rings are called


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annual rings because they grow seasonally and they help a plant to undergosecondary thickening. Generally adult pines have needle-shaped leaves whichare green and photosynthetic. The leaves are in bundles or clusters. The leaves(cotyledons) on seedlings are borne in a whorl of 424. Juvenileleaves, which follow immediately after seedlings, have single, green leavesarranged spirally on the shoot. They also have non- photosynthetic scaleleaves, similar to bud scales. They are arranged spirally like the juvenileleaves.

Cones A cone is an organ of pines that contains the reproductive structures. The woody cone is the female cone, which produces seeds. The male cones, whichproduce pollen, are usually herbaceous and much less conspicuous.

The advantages and disadvantages of the Division Coniferophyta

Advantages of Conifers

1. Conifers are very important for our economy because of their softwood, which is used for paper and timber, as well as cedar which many people usefor their homes because of its beauty and resistance to insects. They have alarge economic use as softwood in furniture. In temperate and tropicalregions, they are fast-growing softwoods that will allow harvesting in closesuccession.

2. Decoration and ceremony Many pine species make attractive ornamentals. They are planted in parks andlarger gardens. Some varieties are suitable for smaller spaces. Pines are alsocommercially grown and harvested for Christmas trees.

3. As medicine, Pines and cypress are rich in vitamin; their branches conesand oils can be extracted and used as nutrient supplements.

4. Due to its soft texture conifers are widely used to manufacture Play wood. 5. As other higher plants conifers are source of heat energy, used asfirewood and charcoal. 6. Thick forests of conifers form green belts that modify the climate. 7. Conifers form a large arena for Biological research Ecological studies. 8. Food uses: Some species have large seeds, called pine nuts that areharvested and sold for cooking and baking. The soft, moist, white inner bark(cambium) found clinging to the woody outer bark is edible and very high in


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vitamins A and C. It can be eaten raw in slices as a snack or dried and groundup into a powder for use as bread flour. Also White Pines are rich in Vitamin Aand C; flour can be made from the Pine tree's inner bark. By chewing bark ofpine you can eliminate bad breath. Pines can reduce the pain of skin infections by applying warm pine sap.

Division Angiospermophyta ( Flowering Plants )

Angiosperms are flowering plants under kingdom Plantae and division Angiospermophyta. This group of plants is sometimes called Magnoliophyta. Angiosperms are the most abundant land plants. Like gymnosperms,angiosperms are seed-producing plants but they are distinguished fromgymnosperms by their characteristic of producing flowers. These plantsproduce fruits that contain seeds instead of cones like it is in gymnosperms.The term angiosperm means a plant that produces seeds within fruits.

Angiosperms life cycleThe ovary has ovules that contain mega-sporocyte. Mega-sporophyte has fourhaploid megaspores; three megaspores disintegrate and the remaining onedivides by mitotic divisions to produce eight nuclei in an embryo sac. Thethree nuclei are organized into the egg whereby one cell is the egg cell; the twoothers are egg helpers. Although these three cells look are similar, only the eggcell continues to develop to an embryo sac. The embryo sac at this stage is thefemale gametophyte or mega-gametophyte.

Pollination and fertilizationThe pollen from the anther is transported to the stigma of a flower. In thestigma pollen tube emerges. The mature male gametophyte therefore is agerminated pollen grain, pollen tube and three sperm nuclei. The pollen tubegrows downward toward the ovary through the style and penetrates theembryo sac. After discharging its contents one of the sperm nuclei fuses withthe egg nucleus and form a zygote, the other sperm fuses with the polar cell ofthe ovary, forming the endosperm nucleus. This is what is known as doublefertilization. Fertilization in angiosperms begins very soon after pollination.Note: In gymnosperms, fertilization can occur up to a year after pollination.

Double fertilization Double fertilization is a distinctive characteristic of the angiosperms andresults in a polyploid endosperm tissue. In double fertilization each ovulereceives a pollen tube that delivers two sperm cells to the embryo sac. Onesperm fertilizes the egg cell to form the diploid zygote, while the other sperm


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They have conducting tissues phloem and xylem. Unlike gymnosperms which have xylem tracheid angiosperms has xylem vessels. The Classes of the Division Angiospermophyta and their distinctive features Division Angiosperms is divided into two classes which are Monocotyledonaeand Dicotyledonae. These two classes are distinguished from each other bytheir morphology and anatomy.

Features of Class Monocotyledonae Monocots have one cotyledon (or one seed leaf) Monocots have broad leaves with parallel venation. Monocots have fibrous root systems. The floral parts in monocots occur in threes, or multiple of three.PMonocots lack cambium secondary growth. Monocots have scattered vascular bundles in their stems.Typicalexample of monocot is a maize plant. Features of Class Dicotyledonae Dicots have two cotyledons (or two seed leaves). Dicots have net venation. Dicots have tap root system Dicots floral parts occur in fours and fives and multiple of four or five. Dicots have cambium secondary growth. Dicots have vascular bundles arranged into a ring. A Typical example ofdicot is a bean plant. Advantages and disadvantages of Division Angiospermophyta Advantages of Angiosperms Agriculture. Agriculture depends on angiosperms. Angiosperms providehuman food. Example; plants belonging to grass family (grains), are the mostimportant food stocks. They include rice, maize, wheat, barley, millet, sugarcane and sorghum. Legume provides beans, several varieties of nuts and soy. Also of potatoes, tomatoes, and peppers, pumpkins, melons and varieties of vegetables to include cabbage and lettuce. Many fruits oranges, lemons andgrapefruits are angiosperms. Livestock. Plants belonging to grass family are the world number onefeeds of livestock. Many types of grassland in Africa are either grazed by cattleor wild animals. Also almost all feeds consumed by human are also used bydomestic animals as food. Wood. Angiosperms provide different varieties of wood for furniture,paper and building materials. Carpentry and masonry depends largely onangiosperms for both soft and hard wood. Textile. Different varieties of fibers including cotton, flax, and hemp areimportant raw materials for textile industry. Cotton is the word first classmaterial for clothes.


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Medicine. Many organic drugs are coming from angiosperm herbs. Theyare either industrial made or can be utilized in its raw form. Today it is believed that herbs form the best medicine when used in their fresh form than when industrial made. Floriculture. Flowers from angiosperms have great social significance asthey are used in different kinds of ceremony. Roses for instance are the mostsold flowers and they are highly purchased and used in wedding and burialceremonies. Forestry. Forestry is the field of study whose base depends on bothangiosperms and gymnosperms. Many forests form green belts that habitdifferent varieties of plants. Ecology. Angiosperms provide a wide range of habitats for differentspecies of organisms. They also serve as primary producers of energy. Climate. Angiosperms are used to modify climate. Green belts areestablished in order to absorb carbon and reduce global warming. Tourism. Many sites of tourism are plants oriented. Ecotourism forinstance depends largely on different plant species that host different kinds ofland animals. Disadvantages of Angiosperms Toxins. Some plants are poisonous when eaten by human and otheranimals. They cause death to human and other living organisms. Somecassava varieties are a good example. They have cyanide acid that inhibitscellular respiration. Drugs. Some angiosperm varieties are drugs that can be abused whentaken. Examples are marijuana, cocaine, tobacco and some caffeine varieties. Weeds. Some angiosperm varieties are bad weeds; they reduce crop yields. Some weeds are parasites. Example, Cuscuta kilimanjari is parasitic tocoffee plantations.

GENETICS What is genetics?

The study of heredity and the variation in living organisms is called genetics. Genetics deals with the molecular structure and function of genes. It is thestudy of heredity, the process in which a parent passes certain genes to theirchildren. Characteristics passed from parents to offspring include height, colorand shape. Those characteristics are determined by genes.

Common terms used in Genetics

Gene.


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opportunities to establish hydrogen bonds between them. Between A and Tthere are two hydrogen bonds and between C and G there are three hydrogen bonds. Chemical structure Types of bases in a DNA

Purine bases: PAdenine and guanine are purines. Purines are the largerof the two types of bases found in DNA. Notice that purines have double rings. Pyrimidine Bases: Cytosine and thymine are pyrimidine bases. Noticethat pyrimidines have single rings.

DNA Backbone The backbone of the DNA strand is made from alternating phosphate andsugar residues. The sugar in DNA is a pentose meaning five-carbon sugar chemically knownas 2-dioxyribose sugar. So, Purine and Pyrimidine bases are strengthened bythis backbone. There are two hydrogen bonds between A & T and three between C & G.These relationships are often called the rules of Watson-Crick base pairing. The rules of base pairing tell us that if we can "read" the sequence ofnucleotides on one strand of DNA, we can immediately deduce thecomplementary sequence on the other strand.Chargaff's rule

Difference between Deoxyribonucleic Acid (DNA) and Ribonucleic Acid (RNA) Differences between RNA and DNA in terms of chemical structure:

DNA is double-stranded while RNA is a single-stranded molecule. RNA has a much shorter chain of nucleotides. DNA contains deoxyribose while RNA contains ribose. In deoxyribosethere is no hydroxyl group in carbon number 2. Presence of hydroxylgroup makes RNA less stable than DNA because it is more prone tohydrolysis. RNAs complementary base to adenine is uracil instead of thymine as itis in DNA. RNA structure RNA strands have a backbonemade from groups of phosphates and ribose, to which four bases can attach.The four bases are adenine, cytosine, guanine, and uracil. Unlike DNA, RNAconsists of a single strand, it contain uracil instead of thymine. In RNAadenine and guanine are purines while cytosine and uracil are pyrimidines. Animportant structural feature of RNA that distinguishes it from DNA is thepresence of a hydroxyl group.


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Mendelian's first law: The law of segregation The Law of Segregation states that every individual possesses a pair of allelesfor any particular trait (characteristic) and that each parent passes a randomlyselected copy (allele) of only one of these to its offspring.

Mendelian's second law: The Law of Independent Assortment The Law of Independent Assortment, also known as "Inheritance Law", statesthat separate genes for separate traits are passed independently of oneanother from parents to offspring. It means that alleles of different genesassort independently of one another during gamete formation.

Illustrate monohybrid crosses and interpret their results of crosses and ratiosMonohybrid crosses and interpret their results of crosses and ratios Interpretdata from monohybrid experiments to demonstrate Mendelian's first law ofInheritance. Interpretation of data from monohybrid experiments to demonstrateMendelian's first law of Inheritance Patterns of Inheritance that follow Mendelian's first law Non-Mendelism Inheritance

A non Mendelian inheritance is a general term that refers to any pattern ofinheritance in which traits do not segregate in accordance with Mendelian'slaws.

Concepts of incomplete Dominance and Co Dominance According to Mendelian's first Law (law of Segregation), every individualpossesses a pair of genes for any particular trait and that each parent passes arandomly selected copy of only one of these genes to its offspring. Accordingto the first law, the two coexisting allele of an individual for each traitsegregate (separate) during gamete formation so that each gamete gets onlyone of the two alleles. Alleles again unite at random fertilization of gametes.

Also Mendel postulated the second law (Law of Independent Assortment) which states that separate genes for 2 separate traits are passed independentlyof one another from parents to offspring. That is, the biological selection of aparticular gene in the gene pair for one trait to be passed to the offspring hasnothing to do with the selection of the gene for any other trait. It means thatalleles of different genes assort independently of one another during gameteformation.

Patterns of Inheritance that deviates from Mendelian's First Law ofInheritance


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There are conditions that deviate from Mendelian inheritance as a result theygive different phenotypic ratios other than those achieved by Mendel formonohybrid cross 3:1 and dihybrid cross 9:3:3:1. Here are the conditions:

Incomplete Dominance in Plants When a homozygous red flowered pea plant is crossed with a homozygous white flowered pea plant, the F1 heterozygotes are found to have pink flowers. When the F1 pink flowered heterozygotes are self-crossed, they produce a F2progeny having identical phenotypic and genotypic ratio of 1 red (RR) : 2 pink(Rr): 1 white (rr). The ratio 1:2:1 does not follow Mendelian monohybridinheritance that gives the ratio 3:1.

If Mendelian first law was to be followed we expected to get 3 flowers red andone white (3:1). However the dominant and recessive allele failed to expressfully their characteristics and another colour (pink) appears to all f1generation. In f2 one flower is red, two are pink and 1 is white giving 1:2:1phenotypic ratio which deviates from 3:1 ratio as per Mendel law . Co-dominance In the phenomenon of co dominance, both dominant and recessive alleles lacktheir dominant and recessive relationships and both have capability to expresstheir characteristics phenotypically in the heterozygous condition. The F1heterozygotes produce an F2 progeny to phenotypic and genotypic ratios of1:2:1 like the incomplete dominance. PFrankly speaking both white and redcolours collaborate in passing their phenotypes to f1 generation hence theterm co-dominance.

In one breed of cattle a genotype of WW will be expressed phenotypically in white coat colour, while the genotype of ww into a red coat colour. When white-coated zebu is crossed with red-coated bull, the F1 heterozygotes arefound to have a phenotype of patches of red and white colour. Gene-Interaction (Epistasis)

When many traits are controlled by more than one pair of genes, aninteraction of these genes affect the phenotype. A recessive allele in one locusmight prevent the expression of a dominant allele at another locus. Example,in sweat peas when two varieties of white plants are crossed, F1 generation haspurple flowers, but among the F2, 9/16 have purple flowers and 7/16 have white flowers. Reason for 9:7 ratio is that if a gene carries recessive allele in itshomozygous form a dominant allele loses dominance power. Lethal gene alleles


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The term Lethal (or lethal gene character) is applied to those changes in thegenes of an organism which produce effects severe enough to cause death.Lethality is a condition in which death of a certain genotype occursprematurely, that is before they produce progenies. In one condition the fully dominant lethal allele kills the carrier individual both in its homozygous and heterozygous conditions. In another condition therecessive lethal allele kills the carrier individual only in homozygouscondition. The lethal alleles modify the 3: 1 phenotypic ratio into 2 : 1

Sickle cell anemia Example of lethal genes in human is Sickle cell anemia. Sickle-cell disease, orsickle-cell anemia, is a genetic blood disorder with incomplete dominance,characterized by red blood cells that assume an abnormal, rigid, sickle shapethat decrease the ability of red blood cells to carry oxygen. Sickle-cell disease,usually occur in tropical and sub-tropical regions where malaria is common.In areas where m alaria is common, there is a fitness benefit in carrying sicklecell trait. Those with only one of the two alleles of the sickle-cell disease aremore tolerant to the infection and thus show less severe symptoms wheninfected.

Sex determination and Inheritance The mechanism of Sex Determination and Inheritance Sex determination

The XY sex-determination system occurs in humans, most other mammals,some insects (Drosophila), and some plants (Ginkgo).

Sex determination involves sex chromosomes X and Y of an individual. Thesex of an individual is determined by a pair of sex chromosomes. Females havetwo of the same kind of sex chromosome (XX), and are called thehomogametic sex. Males have two distinct sex chromosomes (XY), and arecalled the heterogametic sex. The sex determination in humans is principallyinfluenced by fathers than mothers. This is because mother has only XXchromosomes and will always contribute haploid X (according to first law ofMendel). Father contributes either X or Y.

On one hand, whenever father contributes X the child will be female becausehaploid X of father will collaborate with haploid X of mother to form diploidXX which is a female child. On the other hand whenever father contributes Ythe child will be male because haploid Y of father will collaborate with haploidX of mother to form diploid XY which is a male child. The concept of Sex Linked, Sex Limited and Sex Influenced Characters


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Sex influenced traits are genes present in both sexes but expressed in only onesex. These genes cause the two sexes to show different phenotypes. Althoughthey are sex limited (male or female) they only affect autosomal traits andtherefore not sex linked (chromosomes). Example these genes instruct maleelephant seals grow gig and like to fight while female elephant seals growsmall and avoid fighting.

Sex limited traits are autosomal genes which are expressed differently inmales and females. Example male pattern baldness occurs more frequently inmen than in women. Another example is breast cancer that occurs morefrequently in women than in men.

Sex linked traits Sex linkage is the phenotypic expression of an allele related tothe chromosomal sex of the individual. This inheritance is in contrast to theinheritance of traits on autosomal chromosomes, where both sexes have thesame probability of inheritance. Since humans have many more genes on theX than on Y, there are many more X-linked traits than Y-linked traits. If a woman is a carrier of an X-linked recessive allele for a disorder and her matedoes not have it, their boys will have a 50% chance of inheriting the disorder.None of their girls will have it, but half of them are likely to be carriers. If aman has an X-linked recessive disorder and his mate does not carry the allelefor it, all of their girls will be carriers. None of their boys will inherit the allele.Only girls receive X chromosomes from their fathers.

Examples of sex linked traits: 1. HaemophiliaHaemophilia is an x-linked genetically inherited recessive disease in whichone or more of the normal blood clotting factors is not produced. This resultsin prolonged bleeding from even minor cuts and injuries. Swollen jointscaused by internal bleeding are a common problem for hemophiliacs.Hemophilia, most often afflicts males.

2. Colourblindness Colour blindness is an X-linked genetically inherited color vision deficiency in which an individual cannot perceive red and green in the same way as people with normal vision. This condition most often afflicts males.

3. Albinism Albinism is a congenital disorder characterized by the complete or partialabsence of pigment in the skin, hair and eyes due to absence or defect of anenzyme involved in the production of melanin. Albinism results frominheritance of recessive gene alleles and is known to affect all vertebrates


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2. Add a few drops of iodine solution.

Note 1. A blue-black colouration indicates the presence of starch due to theformation of a complex. C. Sudan III test for lipids Lipids include oils, fats and waxes. Procedure 1. Add 2 cm3 of oil to 2 cm3 of water to a test tube. 2. Add a few drops of Sudan III and shake. Note 1. Oils are stained red with Sudan III. Since they are less dense than water,they separate out as a red layer on the water surface. D. Biuret test for proteins Egg albumen is a suitable material for Biuret test which tests for the presenceof peptide bonds. When mixed with dilute alkaline copper sulphate solutions,nitrogen atoms in the peptide bonds form a violet complex with copper(II)ions. Procedure 1. Add 2 cm3 of protein solution to a test tube. 2. Add an equal volume of 5% sodium hydroxide solution and mix. 3. Add 2 drops of 1% copper sulphate solution and mix. Note 1. Violet colouration is developed in the presence of protein.2. Biuret reagent can be used directly for detecting the presence of protein without heating.

Biology for Form II-IV Notes

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Transcript of Biology for Form II-IV Notes