Combined Biology PDF Notes

Combined Biology By u/beazerker Cells - Basic unit of life Structure Animal cell Plant cell Plant vs Animal cells Part/Structure Animal cell Plant cell Cell wall Absent Present Vac...

Combined Biology By u/beazerker Cells - Basic unit of life Structure Animal cell Plant cell Plant vs Animal cells Part/Structure Animal cell Plant cell Cell wall Absent Present Vacuole Small & numerous vacuoles Large central vacuole Chloroplasts Absent Present Centriole Present Absent generally Part & their functions Part Function Nucleus Nuclear envelope: separates the content of the nucleus from the rest of the cytoplasm. Nucleoplasm: dense material within the nucleus. Nucleolus: plays a part in the making of proteins in the cell. Chromatin: long strands of DNA. Cytoplasm Site of chemical reactions in the cell. Forms the larger part of the cell, made up of 90% water and contains dissolved protein, sugars and enzymes. Also contains larger suspended particles of fats and many structures called organelles. Mitochondria Rod-shaped structures that carry out cellular respiration to release energy. Energy used to perform cellular activities (membrane visible under a electron scanning microscope) Plasma membrane Plasma membrane is a membrane that surrounds the entire cell. It is partially permeable allowing certain substances to pass through. Cell wall Plant cells are supported by a cellulose cell wall.  Rough endoplasmic reticulum Consist of a network of flattened spaces lined with a membrane. Have ribosomes attached to the membrane. Responsible for the synthesis of protein Smooth endoplasmic reticulum Responsible for the synthesis of fats, steroids and sex hormones. Vacuoles Small numerous and temporary spaces that store substances. Ribosomes Place for synthesising proteins. Can be attached/unattached to the endoplasmic reticulum. Chloroplasts Only found in the cells of green plants. Carries out photosynthesis. (membrane visible under electron scanning microscope) Golgi apparatus Consists of stacks of flattened membranous sacs and vesicles involved in processing packaging and secretion of substances out of the cell Specialised Cells, Tissues, Organs and Systems - Differentiation is the process by which a cell becomes specialised for a specific function. - Tissue - Group of cells with similar structures which work together to perform a specific function - Simple Tissue: cells of the same kind may group together to form a simple tissue - Complex Tissue: contains more than one type of cells grouped together - Organ - Contains more than one type of tissue, all working together for a specific function.  - Organ System - Consists of several organs working together for a common purpose - Organism - Various systems together make up the entire body of an organism. Nutrients Importance of nutrients: 1. Provide energy for vital activities 2. Provide raw materials to make new protoplasm 3. Help organisms stay healthy Functions of water - Solvent for chemical reactions e.g. photosynthesis - Key component of cells, tissues fluids, digestive juices & blood - Regulation of blood temperature - Transportation of dissolved substances by acting as a solvent Carbohydrates - Single sugars (monosaccharides) → cannot be further digested into simpler substances. Can pass through cell membrane and be absorbed into cells - Glucose - Found in plants and animals - Fructose - Common in plants but rare in animals - Galactose - Present in milk sugar in mammals - Double sugars (disaccharides) → two molecules of single sugars bonded together  - Maltose - Glucose + Glucose —Condensation—> Maltose + Water - Maltose + Water —Maltase, Hydrolysis—> Glucose + Glucose - Sucrose - Glucose + Fructose - Non-reducing sugar - Lactose - Glucose + Galactose - Complex carbohydrates (polysaccharides) - Many monosaccharides joined together, produced by the condensation (polymerisation) of many similar molecules to form a long molecule Polysaccharide Structure Role Occurrence Starch Several thousand Storage form of carbs Found in storage glucose molecules in plants. Can be organs, e.g. potato joined together broken down to tubers and tapioca glucose to provide energy for cell activities Cellulose Many glucose Cellulose cell wall Present in cell walls molecules joined protects plant cells of plants together. The bonds from bursting or between the glucose damage units are different from that in starch. Glycogen Branched molecule Storage form of Stored in the liver made of many carbohydrates in and muscles of glucose molecules mammals. When mammals joined together needed, it is broken down to glucose to provide energy for cell activities. Fats - Organic compounds containing carbon, hydrogen & oxygen, with much less oxygen as compared to hydrogen - Properties & functions - Compact and insoluble in water - Stored as droplets inside cells because they are insoluble and do not affect water potential in cells - Energy store - Triglyceride (fat) contains a greater number of carbon-hydrogen bond per gram than starch or glycogen, so one gram of triglyceride yield about twice as much energy compared to one gram of carbohydrates - Carbohydrates are still the most direct source of energy in living things as they are mobilised much more quickly compared to fats - Common food storage in animals in cold climates - During cold seasons, hibernating animals store fats as food reserve as it is difficult for animals to hunt food - Conduct heat slowly - Mammals have specialised cells for storing fat under the skin; cells are grouped together to form adipose tissue - Function as an excellent heat insulator against heat loss from deeper regions of the body to the outside - Less dense than water - Large animals that live in cold seas such as whales and seals, often have very thick layers of adipose tissue called blubber - Gives buoyancy to aquatic animals - Both the heat insulation and buoyancy help these animals to survive in this environment. - Absorb shock - Acts as a protective layer around delicate and vital organs  - Important component of myelin sheath in nerve cells and cell membrane - Act as an electrical insulator, allowing rapid transmission of electrical impulses along myelinated neurons - An essential component of the cell membrane - Acts as a solvent - Acts as a solvent for fat-soluble vitamins and other vital substances Proteins - Proteins are made up of the elements carbon, hydrogen, oxygen and nitrogen. Sulfur is sometimes present - Proteins are built up from amino acids - Each type of protein has a unique three dimensional conformation → diverse functions - When heated, the weak bonds in the proteins are broken, and the protein is denatured Structure of amino acids: - Amino acids are monomers of protein - 20 naturally occurring amino acids Formation of polypeptide: - Amino acids join together by a peptide bond to form a polypeptide through condensation reaction Formation of protein: - Polypeptide fold into a specific conformation depending on interactions between its amino acid side chains Functions of protein: - Used in the synthesis of new cells, for growth and repair of worn-up cells - Serve as biological catalyst to speed up chemical reactions, e.g. enzymes - Serve as chemical messengers, e.g. hormones such as insulin - Serve a transport function, e.g. haemoglobin is used to transport oxygen in red blood cells - Perform a structural function, e.g. collagen is a component of skin, bones while keratin is a component of hair, nails, and feathers - Used for the defence of the body, e.g. antibodies which recognise and combine with foreign substances such as bacteria - Source of energy during starvation and are oxidised after all the carbohydrates and lipids are used up Food Tests Benedict’s Test - Tests for the presence of reducing sugar - Sucrose is the only common non-reducing sugar among the monosaccharides and disaccharides 1) Add equal volume of Benedict’s solution to 2 cm 3 of solution to be tested 2) Shake the mixture 3) Place test tube in boiling water bath for five minutes 4) Observe precipitate formation and colour changes Results: Blue solution turns: Blue (absent) → Green (little amount) → Yellow (moderate amount) → Orange → Brick-red (most) *Colour change due to precipitate form. Ppt will settle at the bottom after some time Iodine Test - Tests for the presence of starch 1) Place food substance on a white tile. Solid foods may need to be chopped up into smaller pieces. 2) Add 2-3 drops of dilute iodine solution to the substance to be tested 3) Observe colour changes, if any Results: Solution changes from yellowish-brown to blue-black colouration → Starch present Solution remains yellowish-brown → Starch absent Biuret Test - Tests for the presence of protein 1) Add 1 cm 3 sodium hydroxide solution to 2 cm3 of food solution 2) Shake thoroughly 3) Add 1% copper (II) sulfate solution, drop by drop, shaking after every drop until a colour change is observed. Results: Solution changes from blue to violet → Protein present Solution remains blue → Protein absent Ethanol Emulsion Test - Tests for the presence of fats/oil - For liquid food mixture 1) Add 2 cm3 of ethanol to the substance in a dry test tube 2) Shake the mixture thoroughly 3) Add 2cm3 of water to the mixture - For solid food mixture 1) Chop solid food into small pieces and place into a dry test tube 2) Add 2 cm3 of ethanol and shake thoroughly 3) Allow the solid particles to settle 4) Decant the ethanol into another test tube containing 2cm3 of water Results: White emulsion formed → Fats/oil present Solution remains colourless → Fats/oil absent. Enzymes - A protein that functions as a biological catalyst. They can alter or speed up chemical reactions. They remain chemically unchanged at the end of the reaction. - Enzymes can build up or break down complex substances Characteristics of enzymes: 1. Speed up chemical reactions - By lowering the activation energy needed to start a reaction. 2. Required in minute amounts - Enzymes remain chemically unchanged after catalysing a reaction. The same enzyme molecule can be used over and over again, thus a small amount of enzyme can catalyse a large number of chemical reactions. 3. Specific in action - Due to their active sites being complementary to only one type of substrate, enzymes are highly specific in action. Due to this enzyme specificity, each chemical reaction inside a cell is catalysed by a unique enzyme Lock & key hypothesis - The shape of the substrate is complementary to the specific conformation of the active site of the enzyme, such that the substrate(s) can fit exactly - The substrate acts as a “key” while the enzyme is a “lock” - The substrate binds to the active site of the enzyme, forming an enzyme-substrate complex - Once the products are formed, they no longer fit into the active site of the enzyme and are released back into the surrounding medium. - Enzyme is free to bind with other substrate(s) Factors Factors affecting rate of enzyme-catalysed reaction 1. Temperature - Enzymes have an optimum temperature at which the enzyme activity is at its maximum. *Different enzymes have different optimum temperatures, with most ranging from 37-45℃ - At low temperature: - Rate of enzyme activity is low - Enzymes are inactive at low temperatures - From low to optimum temperature - As temperature increases, kinetic energy of substrate and enzyme molecules increases - This increases the frequency of effective collisions between enzyme and substrate molecules and the rate of formation of enzyme-substrate complexes. Thus, the rate of reaction increases. - Reaction rate doubles for every 10℃ rise in temperature until optimum temperature is reached. - Reaction rate is its maximum at optimum temperature. - Past optimum temperature - As temperature increases beyond optimum temperature, reaction rate starts to decrease - Enzymes are denatured. The enzyme loses its 3D shape and specific active site. Thus, it can no longer bind to the substrate. - As temperature continues to increase, more enzyme molecules become denatured, which causes the rate of reaction to decrease further. * Once an enzyme is denatured, it is irreversible and it cannot regain its function even when temperature is lowered.  2. pH - Enzymes have an optimum pH at which the enzymes activity is at its maximum *Different enzymes have different optimum pH - Any pH that deviates from the optimum pH will cause the rate of reaction to decrease - At extreme pH, the enzyme loses its 3D shape and specific active site. Thus, it is no longer able to bind to the substrate *Denaturation is an irreversible process and once an enzyme is denatured, it cannot regain its function even when pH is back to optimum. 3. Enzyme concentration - At low enzyme concentrations, adding more enzymes increases the rate of reaction. - With more enzymes present, frequency for effective collisions between enzyme and substrate molecules increase - The rate of reaction is directly proportional to the enzyme concentration until increasing enzyme concentration can no longer increase the rate of reaction. - At any one time, the same no of substrate molecules bind with the same no of enzyme molecules → amount of product formed per unit time remains the same - Enzyme concentration is no longer the limiting factor. The rate of reaction becomes constant and reaches a plateau. - At this point, substrate concentration becomes the limiting factor  4. Substrate concentration - At low substrate concentration, adding more substrate molecules increases the rate of reaction - With more substrates present, frequency for effective collisions between enzyme and substrate molecules increase - The rate of reaction increases proportionally with an increase in substrate concentration until increasing substrate concentration can no longer increase the rate of reaction - All enzyme molecules are saturated and being made use of → amount of product formed per unit time remains the same - Substrate concentration is no longer the limiting factor. Rate of reaction becomes constant and reaches a plateau - Enzyme concentration becomes the limiting factor Nutrition in Humans In humans, nutrition consists of 1. Feeding or Ingestion - Food is taken into the body 2. Digestion - Large food molecules are broken down into smaller, soluble molecules that can be absorbed into the body cells. a. Physical digestion: Mechanical break up of food into smaller particles b. Chemical digestion: Breakdown of large food molecules into smaller soluble molecules catalysed by digestive enzymes through hydrolytic reactions 3. Absorption - Digested food substances are absorbed into the body cells 4. Assimilation - Some of the absorbed food substances are converted into new protoplasm or used to provide energy. 5. Egestion (a) describe the functions of main regions of the alimentary canal and the associated organs: mouth, salivary glands, oesophagus, stomach, duodenum, pancreas, gallbladder, liver, ileum, colon, rectum, anus, in relation to ingestion, digestion, absorption, assimilation and egestion of food, as appropriate Digestive System Mouth and buccal cavity - Food enters the body through the mouth. The mouth contains: - Salivary glands - Food in the mouth stimulates secretion of saliva into the mouth. Saliva flows into the mouth via tubes called salivary ducts. - Saliva contains an enzyme called salivary amylase which digests starch to maltose. - The pH of the saliva is neutral. Salivary amylase is most active at this pH. - Teeth - Chewing action of the teeth breaks up large pieces of food into smaller pieces. This increases the surface area to volume ratio of the food so salivary amylase can act on it more efficiently. - Tongue - Helps to mix food with saliva and roll the food into small round masses called boli - Taste buds on the tongue help to identify and select suitable foods. - Boli are swallowed and passed down into the oesophagus via the pharynx  - Peristalsis in the walls of the oesophagus pushes each bolus of food down into the stomach Oesophagus - Narrow, muscular tube that carries food from mouth to stomach - Contains two layers of muscles. These muscles are present along the whole gut from the oesophagus to the rectum. - The two layers of muscles are - Longitudinal muscles, on the outer side of the gut wall - Circular muscles, on the inner side of the gut wall - Both sets of muscles produce long, slow contractions that move food along the gut by peristalsis - Peristalsis is the rhythmic, wave-like muscular contractions in the wall of the alimentary canal. - Enables food to be mixed with the digestive juices, and also pushes or propels the food along the gut. - The circular and longitudinal muscles are antagonistic muscles. - When the circular muscles contract, the longitudinal muscles relax. As a result, the wall of the gut constricts, and the gut becomes narrower and longer. The food is squeezed or pushed forwards. - When the longitudinal muscles contract, the circular muscles relax. The gut dilates, and it becomes wider and shorter. This widens the lumen for food to enter Stomach - Presence of food in the stomach stimulates the gastric glands to secrete gastric juices into the stomach cavity - Peristalsis in the stomach wall churns and breaks up the food. Peristalsis also mixes the food well with gastric juices - Gastric juice is a dilute solution of hydrochloric acid and pepsin - stops the action of salivary amylase by denaturing it - changes the inactive form of the enzyme pepsinogen, in the gastric juice to the active pepsin - provides a slightly acidic medium suitable for the actions of pepsin - kills certain potentially harmful microorganisms in food - Protease (pepsin) digests proteins to polypeptides. - Food normally remains in the stomach for about three to four hours. The partly digested food becomes liquefied, forming chyme. - Chyme passes in small amounts into the duodenum when the pyloric sphincter relaxes and opens. *The pyloric sphincter is located at the place where the stomach joins the small intestine. Liver - The liver secretes bile, which is stored in the gallbladder. Gallbladder - Bile is stored temporarily in high concentration in the gallbladder - Bile flows into the duodenum via the bile duct. Small intestine - Consists of the U-shaped duodenum, the jejunum, and the ileum - Chyme stimulates the pancreas to secrete pancreatic juice. Pancreatic juice contains the enzymes pancreatic amylase, pancreatic protease (trypsin), and pancreatic lipase. The pancreatic juice passes through the pancreatic duct into the duodenum. - Gall bladder to release bile. Bile does not contain enzymes so it cannot digest good, but bilt salts speed up the digestion of fats. Bile passes through the bile duct into the duodenum - Epithelial cells in the small intestine produce the enzymes maltase, peptidases and lipase. - Food comes into contact with pancreatic juice, bile and intestinal juice - All three fluids are alkaline - Neutralise the acidic chyme - Provide a suitable alkaline medium for the action of the pancreatic and intestinal enzymes. Large intestine - Consists of the colon and the rectum.  - The main function of the colon is to absorb water and mineral salts from the undigested food material. No digestion occurs in the large intestine. - Faecal matter is temporarily stored in the rectum. When the rectum contracts, the faeces is expelled through the anus. - Digestion of food Carbohydrate digestion - In the mouth & small intestine - Starch is digested by amylase into maltose - In the small intestine - Maltose is digested by maltase into glucose - Lactose is digested by lactase into glucose and galactose - Sucrose is digested by sucrase into glucose and fructose Protein digestion - In the stomach - Some protein is digested by pepsin into polypeptides - In the small intestine - Undigested protein is digested by trypsin into polypeptides - Polypeptides are further digested by peptidases into amino acids Fat digestion - In the small intestine - Bile salts emulsify fats by breaking it up into tiny fat droplets, which increases surface area to volume ratio for increased rate of digestion - Emulsified fats are digested by pancreatic and intestinal lipases to fatty acids and glycerol Absorption Adaptations in the small intestine Adaptations Functions Small intestine is long Provide sufficient time for absorption to take place Small intestine is lined with many villi, each To increase surface area to volume ratio for possessing numerous microvilli absorption of digested food particles Epithelium of the villus is one cell thick To reduce the distance for digested products into the blood vessels Small intestine consists of a dense network of Continuous transport of digested food blood capillaries and lymphatic capillaries substances maintains the steep concentration within the intestinal walls and villi gradient for fast absorption of digested particles Transport and assimilation Assimilation is the process whereby some absorbed food substances are converted into new protoplasm or used to provide energy Glucose - Blood capillaries from the small intestine join together to form the hepatic portal vein, which transports nutrients to the liver - Oxidised during tissue respiration to release energy for the vital activities of the cells - Excess glucose is returned to the liver and stored as glycogen. - Insulin stimulates the liver cells to convert excess glucose into glycogen - Glucagon stimulates the liver to convert glycogen back into glucose Amino acids - Amino acids which enter the cells are converted into new protoplasm that is used for growth and repair of worn-out parts of the body - Amino acids are used to form enzymes and hormones - Excess amino acids are deaminated in the liver Fats - Fats are absorbed into the lymphatic capillaries - The lymphatic capillaries join to form larger lymphatic vessels, which discharge fats into the bloodstream - Under normal conditions when there is a sufficient supply of glucose, fats are not broken down, but are used to build protoplasm - When glucose is in short supply, fats are broken down to provide energy needed by the body - Excess fats are stored in the adipose tissues beneath the skin and around the heart and kidneys. They act as shock absorbers. Liver Functions 1. Regulate blood glucose - Keep amount of glucose in blood constant, especially after a heavy meal or during fasting - Insulin secreted by pancreas stimulates liver cells to convert glucose into glycogen - Glucagon secreted by pancreas stimulates liver cells to convert glycogen into glucose 2. Produce bile - Liver secretes bile, that is stored temporarily in the gallbladder 3. Iron storage - Liver breaks down haemoglobin in red blood cells, and stores the iron that is released - Bile pigments are formed from the breakdown of haemoglobin 4. Protein synthesis  - Liver synthesise protein found in blood plasma from amino acids in the diet. Plasma proteins include prothrombin and fibrinogen which are essential for clotting of blood 5. Deamination of amino acids - Amino groups are removed from amino acids and converted to urea - Excess amino acids are transported to the liver, where they are deaminated and converted to urea - Urea is removed from the body in urine 6. Detoxification - Converting harmful substances into harmless substances - Liver cells contain alcohol dehydrogenase, which breaks down alcohol to acetaldehyde. Acetaldehyde can be further broken down into compounds used for respiration to provide energy for cellular activities Excessive Alcohol Consumption - Cirrhosis of liver, where liver cells are destroyed and replaced with fibrous tissue, making the liver less able to function - Patients with alcoholic cirrhosis may haemorrhage or have bleeding in the liver - This can lead to liver failure, and subsequently, death Harmful effect - Depressant - Reduced self-control - Increased reaction time - Social implications - Alcohol dependence - Neglect work & families - Commit more crimes Nutrition in Plants Photosynthesis - Process in which light energy absorbed by chlorophyll is converted into chemical energy. The chemical energy is used to synthesise glucose from water and carbon dioxide, and oxygen is released as a by-product Word equation Carbon dioxide + Water –Chlorophyll & Light energy→ Glucose + Oxygen Fate of glucose - Used during respiration to release energy for cellular activities - Form cellulose cell wall - Reacts with nitrates and other mineral salts from the soil to form amino acids in leaves. Amino acids form proteins for new cellular materials - Converted into triglycerides (fat) and lipids for storage and synthesis of cell membrane - When rate of photosynthesis is higher than the rate of respiration, excess glucose is - converted into starch for storage. When photosynthesis stops, starch is converted back to glucose for usage - Converted to sucrose for transport to other parts of the plant via the phloem Factors affecting rate of photosynthesis 1. Light intensity - Compensation point is where rate of Ps equals rate of respiration - As light intensity increases during the morning and fades during the evening, there will be a time when the rate of photosynthesis exactly matches the rate of respiration. - This is the compensation point: there will be no net intake or output of carbon dioxide or oxygen - The glucose produced by photosynthesis exactly compensates for the glucose broken down by respiration - As light intensity increases, the rate of the light-dependent reaction, and thus photosynthesis, increases proportionally - As light intensity increases beyond a certain point, the rate of photosynthesis is limited by some other factors such as temperature and carbon dioxide concentration 2. CO2 conc - An increase in the carbon dioxide concentration increases the rate of photosynthesis up to a certain point - Beyond this point, when the concentration of carbon dioxide increases, the rate of photosynthesis plateaus - Rate of photosynthesis is limited by another factor such as light intensity or temperature. Carbon dioxide is no longer the limiting factor. - Under normal circumstances, carbon dioxide is an important limiting factor since atmospheric carbon dioxide remains constant at about 0.03% 3. Temperature - Photosynthesis is dependent on temperature as it is an enzyme-catalysed reaction  - When temperature increases, the kinetic energy of enzyme and substrate molecules increases → frequency of effective collision between enzymes and substrates increases → rate of photosynthesis increases - As the enzymes approach their optimum temperatures, the overall rate of photosynthesis reaches maximum. - As the temperature increases beyond the enzymes’ optimum temperatures, the greater the number of enzyme molecules that are denatured → rate of photosynthesis begins to decrease until it stops → enzymes are denatured Importance of photosynthesis 1. Photosynthesis makes chemical energy available to animals and other organisms - Sunlight is the ultimate source of energy for living organisms. Photosynthesis enables the light energy to be converted into chemical energy which is then stored within carbohydrate molecules. Fats, proteins and other organic compounds can be formed with carbohydrates. - All these substances eventually become the food of other organisms. They thus obtain this chemical energy directly or indirectly from plants. 2. Photosynthesis removes carbon dioxide and provides oxygen - Photosynthesis removes carbon dioxide from the air and at the same time produces oxygen - Oxygen released is used by living organisms in respiration to release energy for cell activities and produce carbon dioxide - This maintains a constant level of oxygen and carbon dioxide in the atmosphere 3. Energy is stored in fossil fuels through photosynthesis - All the energy in fossil fuels like coal, oil and gas, came from the sun, captured through photosynthesis. Burning of fossil fuels releases energy for human activities External features A typical green leaf consists of a lamina and petiole Lamina - The lamina has a large flat surface compared to its volume. This enables it to obtain the maximum amount of sunlight for photosynthesis. A large, thin lamina also means that carbon dioxide can rapidly reach the inner cells of the leaf Petiole - The petiole holds the lamina away from the stem so that the lamina can obtain sufficient sunlight and air. In some leaves, for example grasses and maize, the petiole is absent as they have lone laminae. Network of veins - Veins carry water and mineral salts to the cells in the lamina and carry manufactured food from these cells to other parts of the plant. In a simple leaf, there is a main vein giving off branches repeatedly, forming a network of fine veins. Leaf arrangement - Leaves are always organised around the stem in a regular pattern. In general, leaves grow either in pairs or singly in an alternate arrangement to ensure that the leaves are not blocking one another from sunlight and that each leaf receives sufficient light. Internal structure Cuticle - Waxy and transparent layer - Reduced water loss through evaporation from the leaf and prevents the invasion of bacteria or viruses. - Does not contain chloroplasts Epidermis (upper and lower) - Protects the inner cells and allows light to pass through - Single layer of closely packed cells - Does not contain chloroplasts Palisade mesophyll - Long and cylindrical cells which contain the largest number of chloroplasts for photosynthesis. - Nearest to the upper epidermis and closely packed together. - Filled with chloroplasts. Spongy mesophyll - Irregularly shaped cells which contain chloroplasts for photosynthesis - Loosely packed with large intercellular air spaces among the cells to increase surface area for gaseous exchange - Cells are covered with a thin film of moisture - Contains vascular bundle - Contains less chloroplasts than the palisade mesophyll cells.  - Vascular bundle contains the transport tissues xylem and phloem Intercellular air spaces - Allow circulation of air inside the leaf for photosynthesis and respiration - Interconnecting system of air spaces in the spongy mesophyll allows for rapid diffusion of gases into and out of the cells Guard cells - Contains chloroplasts - Regulates the size of the stomata for gaseous exchange and transpiration. - Cell wall near the stoma is thicker than elsewhere in the cell - In the day: - Guard cells photosynthesise - Chemical energy is used to pump potassium ions into the guard cells from neighbouring epidermal cell - Concentration of K+ ions increases in the guard cells - Water potential in guard cell is lowered - Water from neighbouring cells enter guard cells by osmosis - Guard cells swell and become turgid. - Due to difference in thickness of cell wall in guard cells, one side expands - more than the other. - Stoma opens - In the night: - K+ ions move out of the guard cells by diffusion - Water potential in guard cells increases - Water moves out of the guard cells - Guard cells become flaccid - Stoma closes Adaptations in the leaf for photosynthesis Adaptation Function Petiole Holds leaf in position to absorb maximum light energy Thin, broad lamina Thin lamina provides a short diffusion distance for gases and enables light to reach all mesophyll cells. Broad lamina provides a large surface area for maximum absorption of light.  Waxy cuticle on upper & lower epidermis - Reduces water loss through evaporation from the leaf - Transparent for light to enter the leaf Stomata present in epidermal layers Open in presence of light, allowing carbon dioxide to diffuse in and oxygen to diffuse out of the leaf Chloroplasts containing chlorophyll in all Chlorophyll absorbs and transforms light mesophyll cells energy to chemical energy used in the manufacture of sugars More chloroplasts in upper palisade tissue More light energy can be absorbed near the leaf surface Interconnecting system of air spaces in the Allows rapid diffusion of carbon dioxide and spongy mesophyll oxygen into and out of the mesophyll cells Veins containing xylem and phloem situated Xylem transports water and mineral salts to close to mesophyll cells mesophyll cells. Phloem transports sugars away from the leaf How CO2 enters the leaf - In daylight when photosynthesis occurs, the carbon dioxide in the leaf is rapidly used up - The carbon dioxide concentration in the leaf becomes lower than that in the atmospheric air, setting up a diffusion gradient - Therefore, carbon dioxide diffuses from the surrounding air through the stomata into the air spaces in the leaf - The surfaces of the mesophyll cells are always covered by a thin film of water so that carbon dioxide can dissolve in it - The dissolved carbon dioxide then diffuses into the cells. How water and mineral salts enter the leaf - The xylem transports water and dissolved mineral salts from the roots to the leaf - Once out of the veins, the water and mineral salts move from cell to cell through the mesophyll cells of the leaf Transport in Humans The Need for a Transport System - Simple unicellular organism rely on diffusion for movement of materials into and out of cell - Complex multicellular organism rely on a transport system to transport materials from one part of the body to another, as cells are located deep into the body far from the external environment - Mammals have developed a transport system consisting of blood vessels, blood and heart Blood Structure & Composition Plasma - Pale yellowish liquid, which is about 90% water and the rest is a complex mixture of various dissolved substances such as - Soluble proteins eg fibrinogen, prothrombin and antibodies - Fibrinogen and prothrombin play an important part in the clotting of blood. These proteins are made in the liver. - Antibodies help to fight diseases - Dissolved mineral salts e.g. hydrogen carbonates, chlorides, sulfates and phosphates of calcium, sodium and potassium. All these occur as ions. *Calcium is essential for blood clotting  - Food substances, eg glucose, amino acids, fats & vitamins - Excretory products eg urea, uric acid & creatinine, CO2 (as hydrogen carbonate ions) - Hormones eg insulin - Plasma transports all these substances, together with the blood cells, around the body. The amount of soluble proteins, mineral salts and glucose in the blood plasma are kept relatively constant Red blood cells (RBCs) - There are about 5 million red blood cells in each cubic millimetre of blood. Each red blood cell: - Contains the pigment haemoglobin which combines reversibly with oxygen. It enables RBCs to transport oxygen from the lungs to all cells in the body - Circular, flattened, biconcave disc shape. This increases the cell’s surface area to volume ratio. The cell can thus absorb and release oxygen at a faster rate. - Does not possess a nucleus, enabling it to carry more haemoglobin and thus more oxygen - Elastic and able to turn bell-shaped to squeeze through blood vessels smaller than itself in diameter - RBCs are produced by the bone marrow. Each red blood cell lives for about 3-4 months, before they are destroyed by the spleen. White blood cells - White blood cells are larger than red blood cells but are fewer in number. Each white cell: - Is colourless and does not contain haemoglobin - Is irregular in shape and contains a nucleus - Can move, change its shape and squeeze through the walls of the thinnest blood capillaries into the spaces among tissue cells. - There are two main kinds of white blood cells: lymphocytes and phagocytes. They play a vital role in keeping the body healthy by fighting diseases.  a. Lymphocytes - Has a large, rounded nucleus and a relatively small amount of non-granular cytoplasm. Lymphocytes tend to be nearly round in shape and only show limited movements. They produce antibodies that protect the body from disease-causing microorganisms. b. Phagocytes - Ingest & digest foreign particles such as bacteria Blood platelets - Blood platelets or thrombocytes are not true cells. They are membrane-bound fragments of cytoplasm from certain bone marrow cells. They play a part in the clotting of blood Blood groups Blood group Antigen present on RBC Antigen present in plasma A Antigen A Antibody b B Antigen B Antibody a O No antigen Antibodies a & b AB Antigens A & B No antibodies - Red blood cells have antigens on the surface of their cell membranes - Blood plasma contains antibodies which recognise and bind to specific antigens on the red blood cells of another person - Transfusion of the wrong type of blood causes agglutination or clumping of red blood cells. This could lead to death as the clumps may block up small blood vessels and prevent the flow of blood  - Blood group O is known as the universal donor as there are no antigens on the donor’s red blood cells and thus the recipient’s antibodies would not cause agglutination of the donor’s blood. - Blood group AB is also known as the universal acceptor as there are no antibodies in the plasma of the recipient which could cause agglutination of the donor’s blood Blood Transfusion - A transfusion is the transfer of whole blood or blood components into the bloodstream of another person - Main purpose is to increase blood volume or to improve immunity - Incompatible transfusions can result in agglutination: binding of antibodies in recipient’s plasma to antigens of donated RBCs - Reaction between donor’s antibodies in the plasma and the recipient’s antigens on the RBCs is not significant. Donor’s antibodies are diluted in the recipient’s plasma Functions of Blood Transport function - Blood transports oxygen from the lungs to the cells of the body and carbon dioxide from the body cells to the lungs for removal - Nutrients from alimentary canal to body cells - Glucose and amino acids pass through the liver for processing before entering the general circulation - Metabolic waste from sites of production to sites of removal - Urea produced in liver is sent to the kidneys for excretion, lactate produced in muscles is sent to liver to be broken down - Hormones produced by endocrine glands are transported to target organs  - Insulin stimulate the conversion of excess glucose to glycogen in liver and muscle Substances transported Carried from Carried to Digested food products Small intestines Liver, all parts of the body Nitrogenous waste All parts of the body Kidney Carbon dioxide All parts of the body Lungs Hormones Glands Target cells or organs Heat Respiring body tissue All parts of the body Oxygen Lungs All parts of the body Protective functions - Clotting mechanism - Blood clotting occurs to seal a wound and prevent entry of bacteria and further loss of blood - Involves platelets, plasma protein and other plasma factors - Blood clotting mechanism: 1. Damaged tissues and platelets produce thrombokinase. 2. Thrombokinase converts the protein prothrombin into thrombin in the presence of calcium ions. 3. Thrombin catalyses the conversion of the soluble protein fibrinogen to insoluble fibrin threads. 4. Fibrin threads entangle blood cells and form a clot, sealing the wound  - Defense mechanism - White blood cells protect against disease-causing organisms - Phagocytes carry out phagocytosis to engulf disease-causing organisms - Lymphocytes produce and secrete specific antibodies against disease-causing organisms - Phagocytosis: process of engulfing and ingesting foreign particles - In the process of fighting bacteria, some phagocytes are killed with the bacteria forming pus - Production of antibodies - When pathogens or disease-causing organisms enter the bloodstream, they stimulate lymphocytes to produce antibodies. Antibodies protect our body from diseases by: - Destroying bacteria - Causing bacteria to clump together and be engulfed by phagocytosis - Neutralising the toxins produced by bacteria - Immunisation or vaccination directly induces lymphocytes to produce antibodies by exposing a person to dead or weakened forms of the pathogen - Organ transplant and tissue rejection - A damaged or diseased organ can be replaced by a healthy organ from a donor - Immune system of the organ recipient may treat a transplanted organ as a foreign body. This induces production of antibodies against the organ and results in tissue rejection Regulation of pH, water potential and temperature - Circulating blood maintains homeostasis of body fluids by: - Maintaining an optimum pH in the tissues through the use of buffers - Maintaining the water potential of body fluid - Blood solutes affect the water potential of the blood - Water potential gradient between the blood and the tissue fluid is affected - Water potential is largely due to sodium ions and plasma proteins - Blood solute level regulates the movement of water between blood and tissues. - Water in blood plasma plays a part in the distribution of heat between - The heat-producing areas such as the liver - Areas of heat loss such as the skin Circulatory System Features Artery Capillary Veins Structure Thick, elastic & Capillary wall is a Thinner elastic & muscular walls single layer of muscular walls endothelial cells (relative to artery) Semi-lunar valves (one-cell thick) with absent except in intercellular clefts Semi-lunar valves pulmonary artery & (gaps between cells) present aorta Semi-lunar valves are Branches out into absent arterioles Adaptation to function Function: transport Function: allow for Function: transport blood away from the exchange of nutrients blood towards the heart and waste between heart blood & tissue fluid Thick wall allows the One-cell thick wall Large lumen offer low arterial wall to allows oxygen, food resistance to blood withstand the high and waste products flow → blood can pressure generated to easily diffuse flow smoothly back to by the contraction of through the walls the heart the ventricles. Presence of Semi-lunar valves Muscular wall allows intercellular clefts prevent the backflow for constriction & increase the of blood under low dilation of the artery. efficiency of diffusion blood pressure to When an artery of materials ensure flow of blood constricts, the lumen in one direction  becomes narrower Extensive network and less blood flows surrounding cells through it per unit enable the efficient time. When an artery exchange of dilates, the lumen materials with tissue becomes wider and cells more blood flows through it per unit Blood pressure falls time along the capillaries from the arteriole end Elasticity of the to the venule end due arterial wall enables it to increase in to stretch and recoil cross-sectional area under high pressure. This helps to push the blood in spurts along the artery and give rise to pulse Size of lumen Small lumen relative Very small lumen Large lumen as to diameter of blood compared to the vessel diameter of blood vessel Blood pressure High & pulsatile Blood pressure falls Very low along the capillaries from the arteriole end to venule end due to the increase in cross-sectional area Speed of blood flow Blood flows rapidly, in Blood flows slowly to Blood flows slowly - pulses, reflecting allow more time for skeletal muscles next rhythmic pumping exchange of to the vein assist the action of heart substances to take flow of blood back to place the heart by compressing the veins when muscles contract Direction of blood Flows away from the Flows to cell within Flows from organs flow heart to the organs / organs toward the heart rest of the body tissues Tissue fluid - Tiny spaces between tissue cells contain a colourless liquid, the tissue fluid. The tissue cells are bathed with tissue fluid which carries substances in solution between the tissue cells and the blood capillaries. - Dissolved food substances and oxygen diffuse from the blood in the blood capillaries into the tissue fluid and then into the cells. - Metabolic waste products diffuse from the cells into the tissue fluid and then through the blood capillary walls into the blood. The blood transports these to the excretory organs for removal - Since blood capillaries are narrow, the red blood cells can only move through the lumen of the blood capillaries in a line, one behind the other. The red blood cells may become bell-shaped as they pass through narrow blood capillaries. The advantages of this are: - Diameter of the red blood cell is reduced so that it can easily pass through the lumen of the capillaries. - The cell increases its surface area to speed up absorption or release of oxygen - Rate of blood flow is reduced, giving more time for, and thus increasing the efficiency of exchange of materials between the blood and the tissue cells. Heart Structure - In human beings, the heart is about the size of a clenched fist. It lies in the thorax behind the chest bone and between the two lungs - The whole heart is surrounded by a “bag” called the pericardium. The pericardium is made up of two layers of membrane. The inner membrane is in contact with the tissues making up the heart. Between the two pericardial membranes is a fluid which helps to reduce friction when the heart is beating. - The mammalian heart has four chambers - Atria - The atria have comparatively thin muscular walls since they only force blood into the ventricles and this does not require high pressure. - Ventricles - Ventricles have comparatively thick muscular walls especially the left ventricle, since it has to pump blood around the whole body and this requires high pressure. - The right ventricle has thinner walls than the left ventricle since it only pumps blood to the lungs, which is close to the heart - Median septum - The right and left sides of the heart are separated by a muscular wall called the median septum - The median septum prevents the mixing of deoxygenated blood in the right side with the oxygenated blood in the left side - Mixing of deoxygenated blood with oxygenated blood will reduce the amount of oxygen carried to the tissue cells Path of blood through the heart 1. Deoxygenated blood from various parts of the body is returned to the right atrium. Blood from the head, neck and arms is returned to the right atrium by the superior vena cava. Blood from the other parts of the body is brought back by the inferior vena cava. The superior and inferior vena cava are collectively called the venae cavae 2. When the right atrium contracts, blood flows into the right ventricle. Between the right atrium and the right ventricle is the tricuspid valve, which opens when the pressure in the right ventricle becomes lower than the pressure in the right atrium. It consists of three flaps. These flaps are attached to the walls of the right ventricle by cord-like tendons called chordae tendineae. The flaps point downwards to permit easy flow of blood from the atrium into the ventricle. 3. When the right ventricle contracts, the blood pressure forces the flaps of the tricuspid valve to close. This prevents backflow of blood into the atrium. The chordae tendinae prevent the flaps from being reverted into the atrium when the right ventricle contracts. Blood leaves the right ventricle through the pulmonary arch. The pulmonary arch leaves the heart and divides into two pulmonary arteries, one to each lung. Semi-lunar valves in the pulmonary arch prevent backflow of blood into the right ventricle. 4. Blood in the pulmonary arteries is at a lower pressure than the blood in the aorta. This slows down the rate of blood flow to give more time for gas exchange in the lungs. 5. Oxygenated blood from the lungs is brought back to the left atrium by the pulmonary veins. When the left atrium contracts, the blood pressure in the left atrium becomes higher than that in the left ventricle. This causes the bicuspid valve to open and blood enters the left ventricle. The bicuspid valve separates the left atrium from the left ventricle. This is similar in structure and function to the tricuspid valve except it has two  flaps instead of three. When the left ventricle contracts, blood leaves through a large artery, the aorta. 6. From the aorta, blood is distributed to all parts of the body except the lungs. The aorta curves upwards from the left ventricle as a U-shaped tube. It also possesses semi-lunar valves to prevent backflow of blood into the left ventricle. Blood entering the aorta is at a very high pressure. Two small coronary arteries emerge from the aorta. They bring oxygen and nutrients to the heart muscles. The cardiac cycle 1. The atria contract, forcing blood into the relaxed ventricles 2. After a short pause, the ventricles contract. The rise in pressure causes the atrio-ventricular valves to close to prevent backflow of blood into the atria. This produces a loud ‘lub’ sound. The semi-lunar valves open. Blood flows from the right ventricle and left ventricle into the pulmonary arch and aortic arch respectively. 3. As the ventricles contract, the atria relax. The right atrium receives blood from the venae cavae while the left atrium receives blood from the pulmonary veins. 4. The ventricles relax. The fall in pressure causes the semi-lunar valves to close to prevent backflow of blood from the two arches into the ventricles. This produces a softer ‘dub’ sound. The AV valves also open and blood flows from the atria into the ventricles. 5. The atria contract again and the whole cycle repeats. Pressure change in the heart 1. A slight increase in the ventricular pressure due to the contraction of the left atrium, forcing blood into the relaxed ventricles 2. The ventricle begins to contract, the bicuspid valve closes and the pressure increases 3. The pressure in the ventricle continues to rise as it contracts  4. The pressure in the left ventricle becomes higher than that in the aorta. The semi-lunar valve in the aorta opens 5. The ventricle begins to relax. The aortic valve closes to prevent backflow of the blood into the ventricle 6. The pressure in the ventricle continues to decrease as it relaxes 7. The bicuspid valve opens as the pressure in the ventricle becomes lower than that in the atrium 8. The pressure in the ventricle gradually increases as blood continues to enter the ventricle from the atrium 9. The cycle repeats Main Arteries and Veins of the Body Coronary Heart Disease - The most common heart disease is coronary heart disease - The coronary arteries branch out from the aorta to provide oxygen and nutrients to the heart muscles to sustain it for contractions - Buildup of cholesterol and fatty deposits in the coronary artery wall results in atherosclerosis - Plaque narrows lumen of arteries, resulting in less oxygen and nutrients being supplied to heart muscles  - Patients with coronary heart disease may experience angina - chest pain or discomfort in the area of heart that does not get sufficient blood. - When the coronary arteries are completely blocked, heart attack may occur - When heart tissue does not get any blood flow, the tissue dies, resulting in damage to the heart - Heart attack disrupts the conduction system of the heart and causes sudden death to the patient Factors increasing risk of getting a heart attack - Family history - Being a male - Age - Smoker - High intake of saturated fats and salt - Lack of exercise - High blood pressure - Intake of excessive sugars - High alcohol intake Preventive measures against coronary heart disease - A proper diet is important in reducing the risk of atherosclerosis in the coronary arteries (buildup of plaque in artery) - Substitute food with high saturated fats and cholesterol with polyunsaturated plant fats as they do not stick to the inner surface of the arteries - Proper stress management helps to reduce the risk of a heart attack - Smoking is harmful to the body and should be avoided. Cigarette smoke contains nicotine and carbon monoxide that increase the risk of coronary heart disease - Regular physical exercise has long-term beneficial effects on the circulatory system. It strengthens the heart and maintains the elasticity of the arterial walls. The risk of high blood pressure or hypertension can be greatly reduced Transport in Plants Xylem Structure Function Structural adaptation for function Made up of long and hollow Transport water and mineral Empty lumen without any tubes salts from the roots to the cytoplasm, organelles and stems and leaves in one cross-walls/end walls (cell Made up of dead cells direction walls in between cells). This reduces resistance to the flow of water. Inner walls of vessels are Provide mechanical support Walls are strengthened with strengthened with lignin for the plant. lignin. Prevents the collapse deposits. of the vessel and allows it to provide mechanical support Lignin can deposit in different for the plant. patterns. Phloem Structure Function Structural adaptation for function Made up of sieve tubes Transport manufactured food Pores in the sieve plates (consisting of elongated and substances (sucrose and allow thin-walled sieve tube cells) amino faster flow of manufactured and companion cells. acids) to other parts of the food substances between plant. cells. Sieve tube cells will lose its vacuole, nucleus and most Process of transporting organelles after maturing, manufactured food substances It has degenerate cell (sucrose and amino acids) in contents and a degenerate phloem is known as cytoplasm. transportation. Cross-walls have lots of small pores and are called sieve plates. Companion cells, which lie Mitochondria provides energy  next to sieve tube cells, needed for active transport contain many mitochondria. and for metabolic processes. Vascular Bundle Stem - In a dicotyledonous stem, the xylem and phloem are grouped together to form vascular bundles - The vascular bundles are arranged in a ring around a central region called the pith. - The phloem lies outside the xylem with a tissue called the cambium between them.  - Cambium cells can divide and differentiate to form new xylem and phloem tissues, giving rise to a thickening of the stem. - The region between the pith and epidermis is the cortex. Both the cortex and the pith serve to store up food substances, such as starch. - The stem is covered by a layer of cells called the epidermis. The epidermal cells are protected by a waxy, waterproof cuticle that greatly reduces evaporation of water from the stem Roots - In a dicotyledonous root, the xylem and phloem are not bundled together. Instead, they alternate with each other. - The cortex of the root is also a storage tissue. - The epidermis of the root is the outermost layer of the cells. It bears many root hairs. It is also called the piliferous layer. - Each root hair is a tubular outgrowth of an epidermal cell. This outgrowth increases the surface area to volume ratio of the root hair cell. The absorption of water and mineral salts is increased through this adaptation Transport of water & mineral salts in roots Water - Each root hair grows between the soil particles, coming into close contact with the soil solution surrounding them - The cell sap in the root hair cell is relatively concentrated with sugars and mineral salts. Thus it has a lower potential than the soil solution. Water enters the root hair cells by osmosis. - The entry of water dilutes the sap. The root hair cell now has a higher water potential than the next cell in the cortex. Hence, water moves from the root hair cell to the next cell by osmosis. - Water then travels from cell to cell by osmosis until it reaches the xylem. Ions & mineral salts - Ions and mineral salts are absorbed by active transport, when the concentration of ions in the soil solution is lower than that in the root hair cell sap. - Ions and mineral salts are absorbed by diffusion, when the concentration of certain ions in the soil solution is higher than that in the root hair cell. Adaptations of root hair cell - Root hair is long and narrow. This increases the surface area to volume ratio which in turn increases the rate of absorption of water and mineral salts by the root hair cell. - Cell surface membrane prevents the cell sap from leaking out. The cell sap contains sugars, amino acids and salts. It has a lower water potential than the soil solution. This results in water entering the root hair by osmosis - The root hair cell contains many mitochondria. Aerobic respiration in the mitochondria releases energy for the active transport of ions into the cell. Moving water against gravity Root pressure - Respiring cells around xylem vessels in the roots use active transport to pump mineral salts into the vessels. This lowers the water potential in the xylem vessels, which cause water to move into the xylem vessels by osmosis. This pushes water into the xylem vessels and upwards Capillary action - Water tends to move up very narrow tubes (capillary tubes) due to forces of cohesion (forces of attraction among water molecules) and forces of adhesion (forces of attraction between water molecules and inner walls of the tube) Transpiration - Transpiration is the loss of water vapour from a plant, mainly through the stomata of leaves Transpiration pull - The evaporation of water from the leaves removes water from the xylem vessels. This results in a suction force which pulls water up the xylem vessels. - Main force in drawing water and mineral salts up the plant. 1) Water continuously moves out of the mesophyll cells to form a thin film of moisture over their surfaces. 2) Water evaporates from this thin film of moisture and moves into the intercellular air spaces. Water vapour accumulates in the large air spaces near the stomata (sub-stomatal air spaces). 3) Water vapour then diffuses through the stomata to the drier air outside the leaf. 4) As water evaporates from the mesophyll cells, the water potential of the cell sap decreases. The mesophyll cells begin to absorb water by osmosis from the cells deeper inside the leaf. These cells, in turn, remove water from the xylem vessels. 5) This results in transpiration pull, a suction force which pulls the whole column of water up the xylem vessels. Importance of transpiration: - Transpiration pull draws water and mineral salts from the roots to the stems and leaves. - Evaporation of water from the cells in the leaves removes latent heat of vaporisation. This cools the plant, preventing it from being scorched by the hot sun. - Water transported to the leaves can be used in photosynthesis, to keep cells turgid, and to replace water lost by the cells. Turgid cells keep the leaves spread out widely to trap sunlight for photosynthesis. Factors affecting rate of transpiration 1. Humidity - Higher humidity decreases the rate of transpiration while lower humidity increases the rate of transpiration - Intercellular air spaces in the leaf are normally saturated with water vapour. There is a water vapour concentration gradient between the leaf and the atmosphere. - The drier or less humid the air outside the leaf → the steeper this concentration gradient is → rate of transpiration will be faster. - Increasing the humidity of the air → decreases the water vapour and concentration gradient between the leaf and the atmosphere → rate of transpiration decreases 2. Wind - Higher wind speed increases the rate of transpiration while low/no wind decreases the rate of transpiration - Wind blows away water vapour that accumulates outside the stomata. This maintains the water vapour concentration gradient between leaf and atmosphere. Thus stronger wind results in higher rate of transpiration - In still air, water vapour that diffuses out of the leaf makes the air around the leaf more humid, making the water vapour concentration gradient less steep and decreasing the rate of transpiration. 3. Temperature - Higher surrounding temperature increases the rate of transpiration while lower temperature decreases the rate of transpiration - Assuming that other factors remain constant, a rise in the temperature of the surroundings increases the rate of evaporation of water from the cell surfaces. Thus, the rate of transpiration is greater at higher temperatures 4. Light intensity - Higher light intensity increases the rate of transpiration while lower light intensity decreases the rate of transpiration Wilting - Water lost via transpiration has to be replaced by absorption from the roots. Wilting occurs when the rate of transpiration exceeds the rate of absorption at the roots. - If the rate of transpiration is less than the rate of water absorption, plant cells become turgid and the plant becomes firm and upright. - If the rate of transpiration is more than the rate of water absorption, plant cells become flaccid and plant wilts. - When the leaves fold up, the leaves droop and less leaf surface is exposed to the sun and thus the rate of transpiration decreases. However , rate of photosynthesis also decreases Translocation - Transport of food, such as sucrose and amino acids, in the phloem tissue Respiration in Humans Aerobic respiration - Complete breakdown of food substances such as glucose in the presence of oxygen to release large amounts of energy. Carbon dioxide and water are released as waste products  - Word equation: Glucose + Oxygen → Carbon Dioxide + Water + Large amount of energy Uses for energy in the body - Muscular contractions - Protein synthesis - Cell division & growth - Active transport - Passage of nerve impulses - Maintenance of a constant body temperature Anaerobic respiration - Partial breakdown of food substances in the absence of oxygen. Less energy is released compared to aerobic respiration - Word equation (yeast): Glucose → Ethanol + Carbon Dioxide + Small amount of energy - Word equation (muscle cells): Glucose → Lactic acid + Small amount of energy Breathing during exercise Lactic acid - Anaerobic respiration in muscle cells - During vigorous muscular contractions, the muscle cells first respire aerobically. - Breathing rate increases to remove carbon dioxide and take in oxygen at a faster rate. Heart rate will also increase so that the oxygen can be transported to the muscles at a faster rate. However, there is a limit to the increase in the rate of breathing and heartbeat. - In such cases, muscle cells also respire anaerobically for short durations in order to meet the energy demands of the activity - The extra energy released by anaerobic respiration supplements the energy released by aerobic respiration to allow the muscles to continue contracting. - When anaerobic respiration occurs, there is a buildup of lactic acid in the muscle cells.  - Since there is insufficient oxygen to meet the demands of the vigorous muscular contractions, the muscles incur an oxygen debt. Lactic acid concentrations build up slowly in the muscles, and may eventually become high enough to cause fatigue and muscular pains. The body then needs to rest and recover. - Recovery period - During the period of rest, the breathing rate continues to be fast for some time to provide sufficient oxygen to repay the oxygen debt - Lactic acid is removed from the muscles and transported to the liver - In the liver, some of the lactic acid is oxidised to release energy. This energy is used to convert the remaining lactic acid back into glucose. - When all the lactic acid has been converted to glucose, the oxygen debt is repaid. - Glucose is then transported back to the muscles and the body is ready. Human Respiratory System Nose - Air enters the body through the two external nostrils. - The walls of the nostrils bear a fringe of hairs. The nostrils lead into two nasal passages which are lined with a moist mucous membrane. - Breathing through the nose has the following advantages - Dust and foreign particles, including bacteria in the air, are trapped by the hairs in the nostrils as well as by the mucus on the mucous membrane. - As air passes through the nasal passages, it is warmed and moistened - Harmful chemicals may be detected by small sensory cells in the mucous membrane Nose to Trachea - Air passes into the pharynx from the nose. From the pharynx, air passes into the larynx and then into the trachea through the glottis. Trachea - The trachea (windpipe) is supported by C-shaped rings of cartilage. The cartilage keeps the lumen of the trachea open. The membrane next to the lumen is the epithelium. - The epithelium consists of - Gland cells - Secrete mucus to trap dust particles and bacteria - Ciliated cells - Contain hair-like structures called cilia on their surfaces. The cilia sweep the dust-trapped mucus up the trachea. Bronchi and bronchiole - The trachea divides into two bronchi - Each bronchi carries air into the lung - The bronchi are similar in structure to the trachea. - Each bronchus branches repeatedly, forming numerous bronchioles. - Bronchioles are very fine tubes that end in a cluster of alveoli Alveoli - Gas exchange takes place through the walls of the alveoli. Numerous alveoli are found in the lungs, providing a very large surface area for gas exchange. Adaptations - The numerous alveoli in the lungs provide a large surface area - The wall of the alveolus is only one cell thick, which provides a short diffusion distance for gases, ensuring a faster rate of diffusion - The walls of the alveoli are richly supplied with blood capillaries. The flow of blood maintains the concentration gradient of gases. - A thin film of moisture covers the surface of the alveolus. This allows oxygen to dissolve in it Gas exchange in alveoli - Gas exchange in the lungs occurs by diffusion. Blood entering the lungs has a lower concentration of oxygen and a higher concentration of carbon dioxide than the atmospheric air entering the alveoli in the lungs. - A concentration gradient for oxygen and carbon dioxide is set up between blood and alveolar air. Oxygen diffuses from the alveolar air into the blood capillaries. Carbon dioxide diffuses in the opposite direction. - Oxygen and carbon dioxide concentration gradients between the alveolar air and the blood are maintained by - Continuous flow of blood through the blood capillaries - Movement of air in and out of the alveoli, caused by breathing Path of air into lungs Nostrils → Nasal Passages → Pharynx → Larynx → Trachea → Bronchi → Bronchioles → Alveoli Absorption of oxygen in the lungs 1) One cell thick alveolar wall that separates the blood capillaries from the alveolar air is permeable to oxygen and carbon dioxide 2) Since the alveolar air contains a higher concentration of oxygen than the blood, oxygen dissolves in the moisture lining the alveolar walls and then diffuses into the blood capillaries. 3) Oxygen combines with the haemoglobin in red blood cells to form oxyhaemoglobin. This reaction is reversible. The direction in which the reaction takes place depends on the amount of oxygen in the surroundings. 4) In the lungs where the oxygen concentration is high, oxygen combines with haemoglobin to form oxyhaemoglobin. 5) When the blood passes through oxygen-poor tissues, the oxyhaemoglobin releases oxygen, which will then diffuse through the walls of the blood capillaries into the cells of the tissues. Removal of carbon dioxide from the lungs 1) Tissue cells produce a large amount of carbon dioxide as a result of aerobic respiration 2) As blood passes through these tissues via blood capillaries, carbon dioxide diffuses into the blood and enters the red blood cells. 3) The carbon dioxide then reacts with water in the red blood cells to form carbonic acid. This reaction is catalysed by the enzyme carbonic anhydrase which is present in red blood cells. 4) The carbonic acid is then converted into hydrogen carbonate ions which diffuse out of the red blood cells. Hence, most of the carbon dioxide is carried as hydrogencarbonate ions in the blood plasma. A small amount of carbon dioxide is also carried and dissolved in the red blood cells. 5) In the lungs, hydrogen carbonate ions diffuse back into the red blood cells where they are converted into carbonic acid, and then into water and carbon dioxide. 6) The carbon dioxide then diffuses out of the blood capillaries and into the alveoli, where it is expelled when the body breathes out Breathing Mechanisms in Humans - Inspiration or inhalation is the taking in of air - Expiration or exhalation is the giving out of air. Thoracic cavity (chest cavity) - Chest wall is supported by the ribs. The ribs are attached dorsally to the vertebral column in such a way that they can move up and down. - The ribs are attached ventrally to the sternum. Humans have 12 pairs of ribs but only the first 10 pairs are attached to the sternum. The remaining pairs are free ribs that are not attached to the sternum. - Two sets of muscles, the external and internal intercostal muscles, can be found between the ribs. They are antagonistic muscles. - -Thorax is separated from the abdomen by a dome-shaped sheet called the diaphragm. The diaphragm is made of muscle and elastic tissue. When the diaphragm muscles contract, the diaphragm flattens downwards. When they relax, the diaphragm arches upwards again. The intercostal muscles and the diaphragm change the volume of the thoracic cavity Inspiration 1) Diaphragm muscle contracts and diaphragm flattens 2) External intercostal muscles contract, while internal intercostal muscles relax (RICE) 3) Ribs move upwards and outwards. Sternum moves up and forward. 4) Volume of thoracic cavity increases. 5) Lungs expand and air pressure inside decreases as volume increases. 6) Atmospheric pressure is higher than the pressure within the lungs. This forces atmospheric air into the lungs. Expiration 1) Diaphragm muscle relaxes and diaphragm arches upwards. 2) Internal intercostal muscles contract while external intercostal muscles relax. 3) Ribs move downwards and inwards. Sternum moves down to its original position. 4) Volume of thoracic cavity decreases. 5) Lungs are compressed and air pressure inside increases as volume decreases. 6) Pressure within the lungs is higher than atmospheric pressure. Air is forced out of the lungs to the exterior environment.  Component Inspired air Expired air Oxygen ~21% ~16.4% Carbon dioxide ~0.03% ~4.0% Nitrogen ~78.0% ~78.0% Water vapour Variable (rarely saturated) Saturated Temperature Variable About body temperature (37℃) Dust particles Variable but usually present Little Breathing stimulus: - High concentration of carbon dioxide in the blood - No lack of oxygen. Effects of Tobacco Smoke on Human Health Chemical Chemical properties Effects on body Nicotine a. Addictive drug that a. Increases heartbeat causes the release of rate and blood the hormone pressure. adrenaline. b. Makes blood clot b. Increases risk of easily blood clots in the arteries, which leads to increased risk of coronary heart disease. Carbon monoxide a. Combines with a. Reduces ability of haemoglobin to form blood to carry oxygen. carboxyhemoglobin. b. Increases the rate of b. Narrows the lumen of fatty deposits on the arteries and leads to inner arterial wall, increase in blood which leads to pressure. increased risk of coronary heart disease. Tar a. Causes uncontrolled a. Increases risk of cell division. cancer in lungs. b. Paralyses cilia lining b. Dust particles trapped the air passages. in the mucus lining the air passages cannot be removed, increasing risks of chronic bronchitis and emphysema. Irritants a. Paralyse cilia lining a. Dust particles trapped the air passages. in the mucus lining the air passages cannot be removed, increasing risks of chronic bronchitis and emphysema. 1. Chronic bronchitis - Prolonged exposure to irritant particles that are found in tobacco smoke may cause chronic bronchitis. - The epithelium lining of the air passages becomes inflamed - Excessive mucus is secreted by the epithelium - Cilia on the epithelium are paralysed. Mucus and dust particles cannot be removed. - The air passages become blocked, making breathing difficult. - Persistent coughing to clear air passages, in order to breathe. This increases the risk of getting lung infections.  2. Emphysema - Persistent and violent coughing due to bronchitis may lead to emphysema. - Partition walls between the alveoli break down due to persistent and violent coughing - Decreased surface area for gaseous exchange. - Lungs lose their elasticity and become inflated with air. - Breathing becomes difficult. Wheezing and severe breathlessness result. 3. Lung cancer - Risk of lung cancer increases when a person smokes tobacco - Cancer is the uncontrolled division of cells producing outgrowths or lumps of tissues. Apart from lung cancer, smoking also increases the risk of cancers of the mouth, throat, pancreas, kidneys and urinary bladder. Reproduction in Plants Asexual reproduction - Process producing genetically identical offspring from one parent, without the fusion of gametes. Advantages of asexual reproduction - Only one parent required - Fusion of gametes is not required - All beneficial qualities are passed onto the offspring - Faster method of producing offspring as compared with sexual reproduction - Since organisms are already in a suitable habitat, they can colonise the area rapidly. Disadvantages of asexual reproduction - No genetic variation in the offspring. Hence, species are not well adapted to changes in the environment. Sexual reproduction - Process producing genetically dissimilar offspring, with the fusion of gametes to form a zygote. Advantages of sexual reproduction - Offspring may inherit beneficial qualities from both parents  - There is greater genetic variation in the offspring, leading to species that are better adapted to changes in the environment. Disadvantages of sexual reproduction - Two parents are required (except in plants with bisexual flowers) - Fusion of gametes is required - Slower method of producing offspring as compared to asexual reproduction Parts of a flower - Flowers contain the reproductive organs of flowering plants. - An inflorescence is a cluster of flowers borne on the same stalk - A complete flower consists of - Petals - Modified leaves forming a large part of the flower - The petals combine to form the corolla. - In insect-pollinated flowers, petals - brightly coloured to attract insects for pollination - provide a platform for insects to land. - Sepal  - Modified leaves which enclose and protect other parts of the flower during budding - Pedicel - Flower stalk, connecting flower to the plant - Receptacle - Enlarged end of the flower stalk which bears the other parts of the flower. - Stamen - Male part of the flower - Consists of the anther and filament - Anther - Consists of two lobes and a vascular bundle - Each lobe contains two pollen sacs, which contain pollen grains - Produces pollen grains via meiosis - Splits open to release pollen grains when mature - Filament - Stalk that holds the anther in a suitable position to disperse the pollen - Carpels (pistil) - Female part of the flower - Consists of ovary, a style above the ovary and one or more stigmas - Stigma - Swollen structure at the end of the style that receives the pollen grains - Secretes a sugary fluid that stimulates pollen grains to germinate when mature - Style - Stalk that connects stigma to ovary - Ovary - Develops into a fruit after fertilisation - Produces and protects one or more ovules - Ovule develops into a seed after fertilisation - The ovule produces an ovum by meiosis - The ovule is attached to the placenta by the funicle Self-pollination - Transfer of pollen grains from the anther to the stigma of the same flower or of a different flower on the same plant *NOTE: self-pollination ≠ asexual reproduction - Features favouring self-pollination - Flowers are bisexual with anthers and stigmas maturing at the same time. - Stigma is situated directly above the anthers.  - Advantages of self-pollination - Only one parent plant is required - Offspring inherits its genes from the parent plant. Beneficial qualities are more likely to be passed down to the offspring - It does not depend on external factors such as insects or wind for pollination - Higher chance of pollination to occur as the anthers are close to the stigmas of the same flower. - Less pollen and energy is wasted in self-pollination as compared to cross-pollination. - Disadvantages of self-pollination - Less genetic variation in the offspring as compared to cross-pollination. As a result, the species is less well-adapted to changes in the environment. - Possibility of harmful recessive alleles being expressed in the offspring is higher as compared with cross-pollination. Cross-pollination - Transfer of pollen grains from the anther of one plant to the stigma of a flower in another plant of the same species - Features favouring cross-pollination - Dioecious plants that have either male or female flowers - Bisexual flowers that have anthers and stigmas mature at different times - Stigmas of bisexual flowers may have been situated away from the anthers so that self-pollination is unlikely - Advantages of cross-pollination - Offspring produced may have inherited beneficial qualities from both parents - More varieties of offspring can be produced as there is greater genetic variation. This increases the chance of the species surviving changes in the environment. - Increased probability of offspring being heterozygous - Disadvantages of cross-pollination - Two parent plants are required. - Depends on external factors such as insects or wind for pollination. - Lower probability that pollination will occur. - More energy and pollen is wasted. Insect-pollinated vs Wind-pollinated flowers Insect-pollinated Wind-pollinated flowers Large flowers with brightly-coloured petals to Small, dull-coloured flowers without petals attract insects and provide a platform for insects to land Nectar is present Nectar is absent Flowers are fragrant or sweet-smelling Flowers are odourless Small, compact stigma that do not protrude Large, feathery stigma that protrude out of out of the flower the flower to provide a large SA to trap pollen Stamens are not pendulous and do not Stamens have long pendulous filaments and protrude out of the flower protruding anthers → pollen grains easily shaken out of the anthers Pollen is fairly abundant. Pollen grains Pollen is more abundant. Pollen grains have usually larger with rough surfaces so they can smooth surfaces and are tiny and light → readily cling onto insects’ bodies easily blown about by the wind Nectar guide present on petals to guide Nectar guide absent insects towards nectar Fe