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Nutrition in humans Nutrition: Process by which organisms obtain food and energy for growth, repair and maintenance of the body Peristalsis ○The rhythmic, wave-like muscular contractions in the wall of the alimentary canal ○It enables food to be mixed with digestive jui...

Nutrition in humans Nutrition: Process by which organisms obtain food and energy for growth, repair and maintenance of the body Peristalsis ○The rhythmic, wave-like muscular contractions in the wall of the alimentary canal ○It enables food to be mixed with digestive juices and helps to propel the food through the alimentary canal Antagonistic muscles Circular muscles contract, longitudinal muscles relax -> gut becomes narrower and longer (constricts), causing the food to be squeezed or pushed forward Longitudinal muscles contract, circular muscles relax -> gut becomes wider and shorter (dilates), allowing food to enter the lumen Chemical Digestion Involves the breaking down of large molecules in food, such as proteins, starch and fas, into small, soluble molecules that can be absorbed. This is done with the help of enzymes Physical Digestion Involves the mechanical break up of food into smaller particles Increases the surface area to volume ratio of ingested food so that digestive enzymes can act on the food particles more effectively Following processes: Ingestion Mouth Teeth will cut food up into smaller pieces to increase the exposed surface area of the food Food is taken to amylase into the body Food in the mouth stimulates the salivary glands to secrete saliva Salivary amylase will break down the starch in the food to maltase The tongue will help to mix food with saliva and then roll the food into a bolus, which is  pushed to the back of the mouth then into the oesophagus Oesophagus Peristalsis to move food to the stomach Continued digestion of starch with the salivary amylase from the first step Digestion Stomach Gastric glands secrete gastric juice which contain hydrochloric acid, mucus and the Large food enzyme pepsin molecules are Mucus protects stomach wall from being broken down into digested by pepsin smaller, soluble Presence of food stimulates acid secretion into molecules that the stomach cavity can be absorbed Hydrochloric acid into the body Kill potentially harmful microorganisms in the cells food Acidic pH of 2 as is the ideal pH for the pepsin enzyme Stop the action of salivary amylase by denaturing it Pepsin breaks down the complex proteins into shorter and smaller polypeptides Physical digestion - Peristalsis at the stomach breaks up large food pieces into smaller food pieces Partially digested food forms chyme Small Intestine pH 8 - optimal pH for pancreatic and intestinal (Duodenum) enzymes to function effectively Neutralise the acidic chyme Digestion The food will mix with the bile secreted and the Maltose breaks down the Maltase to glucose Undigested proteins that enter the small intestine are digested by intestinal protease to polypeptides Intestinal protease further breaks down the polypeptides into amino acids Lipase breaks down the lipids into glycerol and fatty acids Note: Pancreatic enzymes are secreted by the pancreas while intestinal enzymes are secreted by the epithelial cells Absorption Small intestine Absorption (ileum) Products of digestion such as glucose, fatty Nutrients move acids and amino acids are absorbed from the small throughout the small intestine, ESPECIALLY intestine into the the ileum bloodstream Glucose and amino acids are absorbed by diffusion and active transport into the blood capillaries of the villi Glycerol and fatty acids diffuse into the epithelium. Here they combine to form minute fat globules that enter the lacteals Water and mineral salts are absorbed by the small intestine and colon Extra: The small intestine absorbs most of this water before the food moves to the colon, where much of the remaining water is absorbed Adaptations 1. Numerous finger-like projections called villi increase the exposed surface area of the small intestine for the higher rate of absorption of digested food 2. Each villus has many blood capillaries which allow blood to transport the absorbed glucose and amino acids away quickly, to maintain a diffusion gradient 3. Each villus contains a lacteal which allows for the rapid transport of absorbed fats away, so a a steep diffusion gradient is maintained 4. The epithelium (wall) of the villus is 1 cell thick so there is a short diffusion distance for digested food to be absorbed into the bloodstream / nutrients to pass through 5. The cells of the epithelium have many microvilli, which further increases surface area for absorption 6. The epithelial cells contain many mitochondria which provide energy for the active transport of nutrients into the villi Colon Absorption of water and mineral salts from undigested food Fermentation of vitamins with colonic bacteria (eg vitamins B and K produced through fermentation) Assimilation Glucose Glucose is assimilated and broken down during cellular respiration Nutrients are to release energy for vital activities of the cells used by cells to Excess glucose is stored as glycogen provide energy  or to make new Protein cytoplasm for Amino acids that enter the cells are converted into new cytoplasm growth that is used for the growth and repair of worn out cells Amino acids are also used to form enzymes and hormones Excess amino acids are deaminated in the liver Fats Fats absorbed into the lymphatic capillaries which join to form larger lymphatic vessels, discharge fat into the bloodstream If there is a sufficient supply of glucose, fats will NOT be broken down but instead used to build protoplasm If there is a short supply of glucose, fats will be broken down to provide the energy needed for the vital activities of the cells Excess fats are stored in adipose tissues found beneath the skin, around the heart and kidney (shock absorbers) Rectum Store faeces temporarily Egestion Anus Egestion occurs When rectum contracts, faeces are expelled through the anus Role of other organs in the digestion process Pancreas ○ Production of pancreatic juice ○ Contains enzymes such as pancreatic amylase, pancreatic protease and pancreatic lipase ○ Pancreatic duct secretes pancreatic juice Bile duct ○ Secretion of bile into the small intestine Bile is released into the duodenum Bile salts emulsify fats by lowering the surface tension of the fat globules to break them up into smaller fat droplets Increases the surface area to volume ratio of the fats for the lipase to act on it Emulsified fats are digested by lipases into fatty acids and glycerol in the small intestine Liver ○ Hepatic portal vein Transport blood rich in amino acids and glucose from the small intestine to the liver ○ Hepatic vein ○ Distribute remaining amino acids and glucose to body parts ○ Hepatic artery Transport blood rich in oxygen to the liver ○ Production of bile  ○ Deamination of amino acids to urea Process by which amino groups are removed from amino acids and converted to urea ○ Detoxification of alcohol and harmful substances like benzoic acid ○ Glucose regulation Effects of alcohol consumption on the brain Temporary effects - drunk driving ○ Increases reaction time ○ Reduced self-control of the person Result in the person deciding to drive faster ○ Blurred vision, poor judgement and poor muscular coordination to react to objects or traffic at a higher speed Long term effects ○ Stimulate secretion of stomach acid -> increased risk of gastric ulcers ○ Develop ‘Wet Brain’ a type of dementia ○ Shrinkage of brain volume ○ Heavy consumption of alcohol during preganncy may intefere with the development of the fetus’ brain ○ Overconsumption of alcohol could lead to liver cirrhosis A disease in which liver cells are destroyed and replaced with fibrous tissue May lead to liver failure and death Societal implications ○ May neglect their work/families ○ May exhibit violent behaviour, especially towards their family ○ May tend to commit crimes Starch Test Benedict’s Test Biuret Test Fats test Observation Conclusion Observation Conclusion Observation Conclusion Observation Conclusion The mixture Starch is Mixture A large The mixture Protein is A milky Lipid is turned from present. turned from amount of turned from present. solution was present. orange to blue to brick reducing blue to formed. blue-black. red. sugar is violet. present. Mixture Starch is Mixture A moderate The mixture Protein is remained not turned from amount of remained absent. orange. present. blue to reducing blue. orange. sugar is present. Mixture A trace turned from amount of  blue to green reducing sugar is present. Mixture Reducing remained blue sugar is absent. Note: Sucrose is NOT a reducing sugar Homeostasis & Hormones Definition: The maintenance of a constant internal environment Stimulus Receptor Negative Feedback process Increase in blood Islets of Langerhans Beta cells from the islets of glucose concentration in the pancreas Langerhans secrete insulin into the from the normal detect the bloodstream increase/decrease in Insulin increases the permeability of the blood glucose the cells to glucose to increase the concentration from uptake of glucose by the cells the normal Increase rate of respiration of the cells increases Insulin stimulates the conversion of excess glucose to glycogen to be stored in the liver and muscle cells (primarily) Blood glucose concentration decreases and returns to normal Decrease in blood Alpha cells from the islets of glucose concentration Langerhans secrete glucagon into the from the normal bloodstream Glucagon stimulates the conversion of glycogen to glucose Blood glucose concentration increases and returns to the normal Increase in water Osmoreceptors in Hypothalamus sends signals to the potential in the blood the hypothalamus pituitary gland to decrease the from the normal detect production and secretion of the increase/decrease in anti-diuretic hormone (ADH) the water potential Decreased ADH decreases the of the blood from the permeability of the cells in the normal collecting duct to water Lower rate of absorption of water from the urine Blood potential in the water returns to  the normal Decrease in water The hypothalamus sends signals to potential in the blood the pituitary gland to increase the from the normal production and secretion of the anti-diuretic hormone (ADH) ADH increases the permeability of the cells in the collecting duct to water Higher rate of absorption of water from the urine Blood potential in the water returns to normal Increase in skin Increase/decrease Arteriole in the skin dilates to allow temperature from the in skin temperature more blood to flow through for higher normal is detected by rate of heat loss thermoreceptors in Sweat gland increase production and the skin secretion of sweat Increased evaporation of water in sweat will help to decrease the skin surface temperature Decrease in skin Hair erector muscle contracts, causing temperature from the hair on the surface of the skin to stand normal Diabetes Definition: A condition where the blood glucose concentration cannot be regulated. Blood glucose concentration exceeds the ability of kidneys to reabsorb all the glucose and glucose is excreted in the urine Type 1 Inherited, Islets of Langerhans unable to produce or secrete sufficient insulin Manage through Regular testing of blood glucose concentrations and urine Watch diet carefully Regular injections of insulin Risk factors of Type 2 diabetes: 1. Obesity a. Liver and muscle cells DO NOT respond well to insulin (muscle resistance) 2. Age a. Liver and muscle cells DO NOT respond well to insulin (muscle resistance) 3. Family history a. Inherited risk 4. Blood lipid levels  a. High levels of ‘bad’ cholesterol LDL and low levels of ‘good’ cholesterol HDL in the blood 5. Sedentary lifestyle a. Physical activities control weight and use up excess glucose, allowing liver and muscle cells to maintain sensitivity to insulin Excretion Definition: Removal of metabolic waste, toxic substances and substances in excess of the body’s requirements Why is excretion necessary? Metabolic activities occur all the time in the body while carrying out life processes to sustain life -> they produce harmful or toxic substances that are NOT needed by the body Metabolic waste products OR excretory products NEED to be removed by the body Main Excretory Products and Their Excretory Organs: Osmoregulation Definition: Maintenance of a constant water potential by controlling the water potential and solute concentration in the blood involving the kidneys and skin Process At the liver, excess amino acids are deaminated to urea Ultrafiltration At the nephrons, as the lumen of the afferent arteriole is larger than the efferent arteriole, the high blood pressure forces small, soluble substances such as water, urea and amino acids into the Bowman’s capsule to form glomerular filtrate At the proximal convoluted tubule, amino acids and glucose are selectively reabsorbed through diffusion and active transport from the glomerular filtrate At the distal convoluted tubule and the loop of Henle, water and mineral salts are reabsorbed At the collecting duct, water is also reabsorbed from the urine  Urine formed will be removed via the urethra Eye Part Function Sclera Tough, white outer covering of the eyeball which is ontinuous with the cornea Protect the eye from mechanical damage Conjunctiva A thin transparent membrane covering the sclera in front Mucous membrane that secrete mucus, thus helping to keep the front of the eyeball moist Eyelashes Help to shield the eye from dust particles Eyelid Protect the cornea from mechanical damage Squnting hlps to prevent too much light from Tear gland Secrete tears Wash away dust particles Keep the cornea moist for atmospheric oxygen can dissolve so that the dissolved oxygen can diffuse into the cornea Lubricate the conjunctiva, helping to reduce friction when the eyelids move Iris Controls the size of the pupil and therefore the amount of light entering the eye Pupil Hole in the centre of the iris that allows light to enter the eye Ciliary body Contains ciliary muscles Control the curvature or thickness of the lens Suspensory ligament Connnective tissue hat attaches the edge of the lens to the ciliary body Aqueous humour / Keeps the front of the eyeball firm and helps to refract light into chamber the pupil Vitreous humour Transparent, jelly-like substance behind the lens Keeps the eyeball firm and helps to refract light onto the retina Cornea Dome shaped layer continuous with the sclera Refract light rays into the eye Causes the greatest refraction of light into the eye Lens Elastic and changes its shape of thickness to focus light onto the retina  Choroid Middle layer of the eyeball Contains blood vessels that will transport oxygen and nutrients to the eyeball and remove metabolic waste products Pigmented black to prevent inner reflection of light in the eye Retina The innermost layer of the eyeball Light-sensitive layer on which images are formed Contains photoreceptors that will produce nerve impulses when stimulated and are connected to nerve endings from the optic nerve Nerve impulses produced will be transmitted from the optic nerve to the brain Fovea Small yellow depression in the retina Where images are normally focused Contains the greatest number of cones but no rods Enables person to have detailed colour vision in bright light Blind spot Region where the optic nerve leaves the eye Does not contain any rods or cones -> Not sensitive to light Cannot see an object if image falls on the blindspot Optic nerve Transmit nerve impulses from the photoreceptors to the brain when the photoreceptors in the retina are stimulated Forming an image on the retina The cornea and aqueous humour refract the light rays onto the lens The lens further refracts and converges the light rays on the retina The image on the retina stimulates the photoreceptors The image formed is upside down, laterally inverted and smaller Nerve impulses are produced by the photoreceptors and transmitted via the optic nerve to the brain The brain interprets these nerve impulses so that we see the object the right way up, front to back and the right size Accommodation / Focusing Adjustment of the lens of the eye so that clear images of objects at different distances can be formed on the retina Far object Ciliary muscles relax, pulling on the suspensory ligament Suspensory ligament become more taut, pulling on the edge of the lens Lens becomes thinner and less convex The lens will refract light onto the retina to produce a focused image of the far object Near object Ciliary muscles contract, relaxing their pull on the suspensory ligaments The suspensory ligament slackens and becomes less taut, relaxing their pull on the edge of the lens Lens becomes thicker and more convex The lens will refract light onto the retina to produce a focused image of the near object Bright light Circular muscles of the iris contract Radial muscles of the iris relax Pupil constricts to reduce the amount of light entering the eye to produce a focused image of ___ on the retina Dim light Radial muscles of the iris contract Circular muscles of the iris relax Pupil dilates to allow more light to enter the eye to produce a focused image of ___ on the retina Advantages of pupil reflex What: A reflex action that is protective in nature 1. Automatic and no learning is required 2. Prevent excessive light from damaging the photoreceptors on the retina 3. Allow sufficient light to enter the pupil so the person can see clearly Binocular Vision  The usage of 2 eyes to perceive a single three-dimensional image of the surroundings The separation between the 2 eyes gives a slightly different view of the world from each retina Our brain fuses the 2 images, so we perceive the relative ad absolute depths of objects in space Nervous System Central Nervous System Brain ○ Integrates visual, auditory, touch, olfactory and taste information from our sensory organs Spinal cord ○ Mostly involved in automatic actions known as reflex actions Peripheral Nervous System Cranial and spinal nerves Sense organs How do the CNS and PNS work together? When there is a stimulus, the receptors in our sensor organs (PNS) are stimulated to produce nerve impulses These nerve impulses are transmitted by nerves (PNS) to the central nervous system The CNS then sends nerve impulses to the effectors, which are either muscles or glands Neurones Sensory neurones Circular cell body One long nerve fibre between the receptor and cell body One short nerve fibre between the cell body and the CNS Motor neurone  Irregular-shaped cell body One long nerve fibre between cell body and effector Relay neurone To relay impulses from sensory neurones to motor neurones Contain many short nerve fibres Synapse Junction between 2 neurones Nerve impulses are transmitted across a synapse by chemicals released by the neurones Reflex action An immediate response to a specific stimulus without conscious control 2 Types: Cranial reflexes - controlled by the brain Spinal reflexes - controlled by the spinal cord  The brain and spinal cord are reflex centres Answering technique (eg touching a hot object) The heat from the object sttimulates the receptors in the skin and nerve impulses are produced The sensory neurone transmits the nerve impulses to the spinal cord to the relay neurone across a synapse. The relay neurone transmits nerve impulses to the motor neurone across another synapse. The motor neurone transmits nerve impulses from the spinal cord to the effector muscle Bicep muscles (effector) contracts and causes the hand to withdraw Sensation Receptor in skin -> sensory neurone -> relay neurone in the spinal cord -> brain Voluntary action Activities that are controlled consciously Brain -> relay neurone in the spinal cord -> motor neurone -> effector Involuntary action Activities that are not controlled consciously Sensory neurone -> relay neurone -> motor neurone Reflex arc The shortest pathway by which nerve impulses travel from the receptor to the effector in a reflex action Receptor -> sensory neuron -> relay neurone (CNS) -> effector -> motor neurone Endocrine vs nervous system Endocrine system Nervous System Both serve as a means of co-ordination within the body. A stimulus causes the transmission of a message to a target organ which carries out the response Uses hormones are messengers Uses nerve impulses as messengers Hormones are transported by blood Nerve impulses are transmitted by neurones Responses may be short-lived or long-lived Responses are usually short-lived Always involuntary May be voluntary or involuntary May affect more than 1 target organ Usually localised Cell structure What does a cell consist of Protoplasm which is made up of ○ Cell surface membrane ○ Cytoplasm ○ Nucleus Part Structure Function Nucleus Nucleolus - large black Chromosomes are made up of dot DNA which carried hereditary Chromosomes information Long thread-like structures found within the nucleus Nuclear Contains pores, known Separate the contents of the membrane/envelope as nuclear pores nucleus from the rest of the Have 2 layers of cytoplasm membranes Golgi Apparatus Consist of 5 to 8 Chemically modifies cup-shaped, series of substances from the ER compartments known as Stores and packages the cisternae (s: cisterna) substance in vesicles for secretion out of the cell or to other organelles in the cell Chloroplasts Oval structures found in Thylakoid membrane contains plant cells chlorophyll, which is required Double membranes for photosynthesis to occur enclose a fluid-filled space called stroma The third inner membrane called thylakoid membrane forms the thylakoid Stacked thylakoid is also known as granum or grana Mitochondria Oval or sausage-shaped Site for aerobic respiration to organelles produce ATP for cellular Presence of double activities membranes surrounding a matrix Presence of cristae (s:crita), the foldings of  the inner membranes Rough endoplasmic Network of flattened sacs Modify proteins made by reticulum lined with a membrane ribosomes The outer surface of rER is continuous with the nuclear envelope rER appears rough because its surface is studded with ribosomes Ribosomes Small around structures Responsible for the synthesis Either attached to the of polypeptides from amino rER or lie freely in the acids cytoplasm (free or bound) Smooth endoplasmic sER is more tubular than Synthesises substances such reticulum rER as fats and steroids Does not have Involved in detoxification of ribosomes attached to its drugs surface Vacuole Fluid filled space Stores substances within the cell enclosed by a partially Plant cells: One large central permeable membrane vacuole Consists of substances such as sugars, mineral salts and amino acids or serve as disposal of waste materials Animal cells: Usually have numerous small vacuoles Store water and food substances Exist temporarily Cytoplasm Where all the organelles are found Where all cell activities take place Cellulose cell wall Regular shape Allow plant cell to maintain a regular shape Remain turgid and prevent plant cell from bursting when there is excess intake of water How cell organelles work together: 1. Nucleus controls the synthesis of polypeptide  2. Vesicles containing polypeptide made by the rER pinch off from the rER 3. Vesicles fuse with the Golgi body releasing the molecules made by the ER which may be modified 4. Secretory vesicles containing modified molecules pinch off from the Golgi body and move towards the cell surface membrane 5. Secretory vesicles fuse with the cell surface membrane and their contents exit the cell Adaptations of other cells Red Blood cells ○ Biconcave shape Increase surface area to volume ratio for higher rate of diffusion of oxygen in and out of the cell ○ Contains haemoglobin Binds to oxygen and transports it around the body ○ No nucleus Allow packing of more haemoglobin for transport of more oxygen ○ Elastic, flexible Able to change shape to easily squeeze through capillaries Skeletal muscle cells ○ Contain many mitochondria Provide a lot of energy in the form of ATP via cellular respiration for contraction of skeletal muscles ○ Has contractile protein fibres Contract and relax to bring about movement ○ Has many nuclei Allow for cell division Root Hair Cell ○ Long and narrow extension Increase surface area to volume ratio for increased rate of absorption of water and mineral salts ○ Maintains a lower water potential in the vacuole Allow water to enter the root hair cell via osmosis Movement of substances Definitions Factors affecting rate Examples Diffusion The net movement of particles from a 1. Diffusion Gas exchange of region of higher concentration to a distance oxygen and region of lower concentration down 2. Surface area carbon dioxide in the concentration gradient across a to volume human lungs selectively permeable membrane. ratio Uptake of gases 3. Concentration in root hair cells Facilitated The net movement of particles from a gradient Diffusion region of higher concentration to a  region of lower concentration down the concentration gradient across a selectively permeable membrane using a transport protein embedded. Osmosis The net movement of water 1. Osmosis Plant support molecules from a region of higher distance Turgor maintains the water potential to a region of lower 2. Surface area shape of soft tissues in water potential down a water potential to volume plants. The young stems gradient across a selectively ratio and leaves of permeable membrane. 3. Water herbaceous plants and potential non-woody plants are gradient able to remain firm and erect. This is because of turgor pressure within the cells Wilting and plasmolysis Cell lysis and crenation Active The net movement of particles from a 1. Diffusion Uptake of glucose transport region of lower concentration to a distance by microvilli or region of higer concentration against 2. Surface area epithelial cells in a concentration gradient across a to volume human small selectively permeable membrane ratio intestines using transport proteins embedded 3. Concentration Uptake of mineral gradient salts by root hair 4. Availability of cells from the soil energy in the (with lower form of ATP concentration of mineral salts) Bulk Net movement of substances in the Dependent Exocytosis - transport form of vesicles across the cell on the needs secretion of surface membrane using ATP as the of the cell enzymes or form of energy Availability of insulin energy in the Endocytosis - form of ATP phagocytosis such as ingestion of white blood cells Pinocytosis - Uptake of nutrients (eg proteins) by microvilli of epithelial cells in human small  intestines How does osmosis affect living organisms? Solution placed Effect on plant cells Effect on animal cells in Lower water By osmosis, there will be a net By osmosis, there will be potential movement of water molecules from the a net movement of water higher water potential of the cytoplasm to molecules from the higher the lower water potential in the solution water potential in the across the selectively permeable cell cytoplasm to the lower surface membrane water potential of the As the cell loses water, the volume of the solution across the cytoplasm decreases selectively permeable cell The cytoplasm shrinks away from the cell surface membrane wall, causing the plasymolysis of the Cell shrinks and spikes plant cell appear on the cell A plasmolysed cell can be returned to its The crenated animal cells OG shape by placing it in water or in a becomes dehydrated and solution with higher water potential will eventually die The cell decreases in size and becomes limp Higher water By osmosis, there will be a net By osmosis, there will be potential movement of water molecules from the a net movement of water higher water potential of the solution to molecules from the higher the lower water potential in the cell sap water potential of the across the selectively permeable cell solution to the lower water surface membrane potential in the cytoplasm Volume of cytoplasm increases across the selectively Cell does not burst because it is permeable cell surface protected by the inelastic cell wall membrane The cell expands and becomes turgid Cell will expand and burst (no cell wall to protect it) Biomolecules Elements present Function Carbohydrates Carbon, oxygen and hydrogen Immediate source of energy General formula: Cx(H2O)y Proteins Carbon, oxygen and hydrogen, Synthesis of cytoplasm for repair and nitrogen and sometimes sulfur growth of new and worn out cells  Lipids Carbon, oxygen and hydrogen Long term storage for energy, provide up to twice the amount of energy carbohydrates do Insulation Carbohydrates Monosaccharides: Fructose Galactose Glucose Disaccharides: Glucose + glucose -> maltose Fructose + glucose -> sucrose Glucose + galactose -> lactose Polysaccharides: Starch - several thousand glucose molecules joined together ○ Storage organs of plants Cellulose - many glucose molecules joined together but bonded differently from starch ○ Cell walls of plants Glycogen - branched molecules of many glucose molecule ○ Stored in the liver and muscles of mammals Benedict’s test is used to test for the presence of reducing sugars (they can reduce Cu(II) ions to Cu(I) ions) Lipids Triglyceride -> 1 glycerol + 3 fatty acids Proteins (Enzymes) Contain: A basic amino group (-NH2) An acidic carbonyl group (-COOH) and a variable R-group Charges of different amino acids ○ Non-polar ○ Polar ○ Positively charged ○ Negatively charged Formation of dipeptide bond Two amino acids react together with the loss of a water molecule (condensation), forming a peptide bond From amino acids to a polypeptide chain Many amino acids condensed together to form a polypeptide Proteins must be folded into a complex and specific 3D shape in order to be functional The synthesis of a polypeptide is not equivalent to the production fo a functional protein Multiple polypeptide chains must assemble into a functional protein complex 4 levels of protein organisation 1. Primary a. Unique number and sequence of amino acids held together by peptide bonds that make up a polypeptide b. Peptide bonds are formed/broken down by enzyme catalysed condensation/hydrolytic reactions 2. Secondary a. Folding and coiling of parts of the polypeptide to form i. Alpha helix ii. Beta pleated sheets 3. Tertiary a. The final unique 3D structure of the polypeptide b. All enzymes have a tertiary structure c. Held together by 4 types of bonds i. Ionic bond ii. Disulfide bond iii. Hydrogen bond iv. Hydrophobic interaction d. Example: Lysozyme 4. Quaternary a. 2 or more polypeptides are involved in forming a complex, biologically functional protein / biologically active molecule b. Example: Haemoglobin - 2 alpha chains and 2 beta chains Definition of a catalyst A substance that can speed up a chemical reaction without itself being chemically changed at the end of the reaction Definition of an enzyme Enzymes are proteins that function as biological catalysts. They catalyse or speed up the rate of chemical reactions Remain chemically unchanged at the end of the reaction Activation energy: Energy needed to start a chemical reaction Key characteristics of enzymes 1. Speed up chemical reactions by lowering the activation energy of the reaction 2. Specific in action  3. Required in small quantities and remain chemically unchanged at the end of the reaction 4. Affected by temperature 5. Affected by pH Lock and key hypothesis - How enzymes work The shape of the active site is complementary to the shape of the substrate Upon effective collisions between the enzyme’s active site and the substrate, the enzyme-substrate complex is formed Interactions between the enzyme and substrate molecules strain/weaken chemical bonds within substrates. Thus, lowering activation every When reaction between substrate(s) and enzymes is completed, product(s) no longer fit into the active site of the enzymes Products are released Factors affecting rate of catalytic activity 1. Temperature Low temperatures Inactive at low temperatures Low kinetic energy of the enzyme Frequency of effective collisions between enzymes and substrates to form enzyme-substrate complexes is low Optimum temperature As temperatures increase, the kinetic energy of the substrate and enzyme molecules increase, thereby increasing the frequency of effective collisions between the substrate and enzyme’s active sites Increases the rate of formation of enzyme-substrate complex and increase the rate of reaction/products formed High temperature At high temperatures beyond the optimum temperature, bonds holding the 3D specific shape of the enzyme will be broken This will cause the active site of the enzyme to lose its specific 3D conformation, hence the active site of the enzyme will no longer be complementary to the substrate The enzyme is denatured and will lose its catalytic function 2. pH Structure of the protein is maintained by various bonds. Changes in pH alter the bonding pattern, hereby altering the specific 3D conformation of the active site of the enzyme Hence the active site of the enzyme will no longer be complementary to the substrate The enzyme is denatured and loses its catalytic function Bioenergetics Energy Living things need a continuous transfer of energy to keep them alive and active Energy is used to build, maintain and repair body structures, and for all activities of life Energy is transferred in cells by the breakdown of nutrients Anabolic pathways Consume energy to build complex molecules from simpler ones Catabolic pathways Release energy by breaking down complex molecules into simpler compounds Energy released by catabolic pathways is used to drive anabolic pathways ATP Small, soluble organic molecule When an ATP molecule is hydrolysed, it loses one of its phosphate groups and energy is transferred - can be used by cells for many metabolic reactions ATP is converted to ADP (useful when we look at photosynthesis later) Each cell makes its own ATP by cellular respiration The hydrolysis of one ATP molecule releases a small amount of energy that is often just the right size to fuel a particular step in a process Why not use glucose? Glucose molecule contains FAR TOO MUCH energy A lot of energy would be wasted if cells used glucose molecules as theri immediate source of energy Plant Structure Parts of the leaf Part Function Leaf blade High surface area to volume ratio Enables it to obtain the maximum amount of light for photosynthesis Large, thin leaf blade also allows CO2 to rapidly reach the inner cells of the leaves Network of veins Consist of xylem and phhloem Leaf arrangement Organised around the stem in a regular pattern Leaves grow either in pairs or singly in an alternate arrangement  Ensures that the leaves are NO blociing one another from light and that each leaf receives sufficient light Leaf stalk Holds the leaf blade away from the stem Ensure that the lead blade can obtain light and air In some leaves, leaf stalk is absent as the leaves have long leaf blades Cuticle Waxy Reduce water loss through evaporation from the leaf Transparent Allow light to enter the leaf Palisade Mesophyll More chloroplasts in upper palisade tissues cells Closest to the sun so can absorb maximum sunlight near the upper leaf surface for the highest rate of photosynthesis Spongy mesophyll Contains cells with an irregular shape cells Numerous large intercellular air spaces among the loosely packed cells Carries out photosynthesis but contains fewer chloroplasts than the palisade mesophyll Cells covered with a thin film of moisture Contains transport tissues - xylem and phloem which are grouped together to form a vascular bundle Adaptation: Chloroplast containing chlorophyll in all mesophyll cells -> chloroplast absorbs energy from light and transfers it to chemical stores of energy in glucose molecules Intercellular air Interconnecting system of air spaces in spongy mesophyll spaces Allow for rapid diffusion of carbon dioxide and oxygen into and out of the mesophyll cells Lower epidermis Consists of a single layer of closely packed cells Stomata (s: stoma) Present in the epidermal layers Open in the presence of light, allowing carbon dioxide to diffuse in and oxygen to diffuse out of the leaf Guard cell Found in the lower epidermis A pair surrounds each stoma and helps to regulate the rate of transpiration by opening and closing the stoma Guard cells contain chlorophyll which are NOT present in other epidermal cells How do guard cells control the size of the stomata? Stomata opens as a result of turgid guard cells ○ Light triggers the active uptake of potassium ions by guard cells from nearby cells  ○ Lowers the water potential of guard cells and water enters by osmosis ○ The uneven thickness of the cells walls of teh guard cells result in the cells bowing with water intake, opening the pore of the stoma Stomata close when water leaves the guard cells by ○ Diffusion of potassium ions out of the guard cells ○ This increases the water potential of the guard cells and water leaves by osmosis ○ The guard cells become FLACCID and the stomata closes How carbon dioxide enter the leaf cells CO2 diffuses into the leaf through the stomata It dissolves in the water around the cells (remember the thin film of moisture on the spongy mesophyll cells) It then diffuses into the cells How do the leaf cells receive water and mineral salts? Water and mineral salts are transported through the xylem vessels from the roots Move from cells to cell through the mesophyll ○ Spongy mesophyll contains the vascular bundle Transport in the plant Part Function Xylem Functions: To conduct water and mineral salts up from the roots To provide mechanical support Walls lined with lignin Provide mechanical support for the plant to withstand negative pressure Long, hollow tube made up of dead cells with no-cross walls Allow for the transport of water without resistance Phloem Function: To conduct manufactured food substances (sucrose and amino acids) from the leaves to other parts of the plant Adaptations: A column of sieve tube cells form a long sieve tube The sieve plates which are ‘cross-walls’ between the cells have many minute pores Sieve tube elements which contain several mitochondria Provide a lot of energy for active transport of the food Difference between xylem and phloem  Feature Xylem Phloem Vessel cells Dead Living End walls broken Completely Partially down Direction of flow Unidirectional - Upwards Bidirectional - up and downwards Process by which Transpiration Translocation substances are moved Describe translocation The sucrose molecules move from the mesophyll cells in the lead to the phloem in the vascular bundle of the lead This is followed by the movement of the phloem in a vascular bundle of the fruit, and finally to the cells of the fruit How is water moved against gravity in plants/how does transpiration work? Evaporation of water from the leaves removes water from the xylem vessels This results in a suction force which pulls the water up the xylem vessels It is the main force that draws water and mineral salts up from plant The stream of water up the plant is called the transpiration stream How is transpiration a consequence of gaseous exchange in plants?  As transpiration occurs mainly through the stomata, it is lined to gas exchange between the plant and the environment During photosynthesis, the plant releases oxygen while simultaneously absorbing oxygen There is a concentration gradient between the environment in the lead and the air around as water vapour is more concentrated in the intercellular air spaces Water vapour diffuses out of the leaf through the stomata Transpiration does not occur when the stomata are closed Guard cells control whether the stomata is open or closed Transpiration pull = suction force due to transpiration Factors affecting transpiration Factor Change in factor Explanation Temperature Increase Increases molecular movement so that more water molecules evaporate from the cell surfaces Rate of diffusion of water molecules from the leaf is increased Humidity Increase Reduces the concentration of water molecules outside the leaf Higher water vapour concentration gradient between the surrounding outside the leaf and the intercellular air spaces Rate of diffusion of water vapour from the leaf increases Air movement Increase Removes water vapour from leaf surfaces Higher water vapour concentration gradient between the surrounding outside the leaf and the intercellular air spaces More water vapour diffuses out from the leaf Light intensity Increase Increase the rate of photosynthesis Increase stomata size for more oxygen to be given out Rate of diffusion of water vapour out of the leaf increases Wilting The turgor pressure in the leaf mesophyll cells helps to support the leaf and keep it firm Enables the leaves to spread out widely to absorb light for photosynthesis Wilting occurs when the rate of transpiration is HIGHER than the rate of absorption of water by the roots Advantages: Reduction in the rate of transpiration due to Reduction in exposed surface area of the leaf to light Reduced exposure of the stomata to the atmosphere Reduced rate of water loss through the stomata Excessive loss of water causes guard cells to become flaccid and stomata to close Disadvantages Closure of stomata reduced amount of carbon dioxide entering the leaf Carbon dioxide becomes a limiting factor Decrease in the rate of photosynthesis Folding of leaf reduced surface area exposed to light Decrease in rate of photosynthesis Photosynthesis Water + Carbon dioxide -light + chlorophyll -> Oxygen + Glucose Why is photosynthesis important? Converts energy from the sun into chemical energy (needed by other organisms) Remove carbon dioxide from the atmosphere Produces oxygen needed for respiration by other organisms Contributes to the energy stored in fossil fuels Products of the light-dependent stage are used to drive reactions in light-independent stage to produce sugars Light dependent reaction Occur at the grana Light energy absorbed by chlorophyll is harnessed for the formation of NADPH and ATP. Light energy is also involved in the photolysis of water molecules to split water molecules to form oxygen gas and hydrogen. Light independent reaction (Calvin cycle) Occur at the stroma Require continuous supply of ATP and NADPH to reduce carbon dioxide to carbohydrate Steps: 1. Carbon fixation  a. Diffusion of carbon dioxide into the stroma b. Carbon dioxide combines with RuBP in the presence of RuBisCO (enzyme) to form GP 2. GP is reduced to triose phosphate (3-carbon sugar) a. By NADPH and ATP b. Energy from ATP and hydrogen from NADPH (oxidation of NADPH to NADP) are used to reduce GP to triose phosphate c. From triose phosphate, carbohydrates (other sugars and starch, and sucrose for translocation), lipids and amino acids can be synthesized 3. Regeneration of RuBP a. RuBP is regenerated using energy from ATP -> so that more CO2 can be fixed Light independent VS light dependent Location Input Output Processes involved Light dependent Grana Sunlight ATP Photoactivation ADP NADPH Inorganic Oxygen Photolysis of phosphate water molecules NADP Water Light Stroma ATP Glucose 1. Carbon fixation independent NADPH ADP 2. Reduction Carbon dioxide NADP 3. Regeneration of RuBP Factors limiting rate of photosynthesis Limiting factors: A factor that affects the rate of reaction. The rate cannot increase unless the value of the liming factor is increased. Light intensity Increase in light intensity More light energy absorbed by the chlorophyll in the leaves Higher rate of formation of ATP and NADPH through the light-dependent reaction With increased ATP and NADPH, a higher rate of reduction of GP to triose phosphate Carbon dioxide concentration Increase in carbon dioxide concentration When carbon dioxide is NO LONGER the limiting factor  Temperature Increase in temperature Higher rate of evaporation of water from the Mesophyll cells to the intercellular air spaces Higher rate of transpiration Size of stomata enlarges Results in greater intake of carbon dioxide and more oxygen released into the environment Increase in carbon dioxide intake (see above) Increase in temperature to optimal temperature for the enzyme RuBisCO to function ○ Increase in kinetic energy of the substrate and RuBisCO ○ More effective collisions between the substrate and enzyme to form enzyme-substrate complex ○ Increase rate of reaction for higher rate of formation of products When the temperature is NO LONGER the limiting factor Enzymes are saturated - all RuBisCo enzymes are occupied by the substrate Since RuBisCo enzymes are unable to increase the rate of formation of products, this would be the highest rate of photosynthesis Beyond the optimum temperature Denaturation of RuBisCO enzyme Respiration in humans Breathing: Involves movement of air in and out of lungs Aerobic Respiration Anaerobic respiration Definition The breaking down of food molecules such as glucose to release energy. Equation Oxygen + glucose -> Carbon dioxide + Glucose -> lactic acid water Similarities Both aerobic respiration and anaerobic respiration involve the breakdown of glucose. Differences Aerobic respiration produces a lot of Anaerobic respiration produces a small energy in the form of ATP. amount of energy. Aerobic respiration requires oxygen as a Anaerobic respiration does not require reactant. oxygen as a reactant. Aerobic respiration occurs at the Anaerobic respiration occurs in the mitochondria. cytoplasm of muscle cells during  vigorous activity. What happens during vigorous activity and why is anaerobic respiration important? Muscles need more energy to contract Aerobic respiration in muscle cells increased ○ There will be an increased breathing rate to obtain oxygen ○ Increased heart rate to supply oxygen When continuous muscle contractions occur ○ Aerobic respiration alone is NOT FAST ENOUGH to supply the increase in energy demand ○ Anaerobic respiration takes place to meet the increased energy demand Oxygen debt is addressed through deeper and faster breathing & fast heart rate ○ Oxygen debt is the amount of oxygen needed to remove lactic acid Why does the build-up of lactic acid in muscles need to be removed? Continued fast heart rate ○ To transport lactic acid to the liver via blood for removal ○ To transport oxygen to the liver Continued deeper and faster breathing ○ To obtain oxygen for supply to the liver Human respiratory system Part Function Nose Dust and foreign particles, including bacteria in the air, are trapped by the nostrils as well as 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 Pharynx Larynx Trachea Supported by C-shaped cartilage rings Cartilage keeps the lumen of the trachea open The membrane next to the lumen is the epithelium which consists of ○ Gland cells Secrete mucus to trap dust particles and bacteria ○ Ciliated cells Have hair-like structures called cilia on their  surfaces Cilia sweep the dust-trapped mucus up the trachea Bronchi and Each bronchus carries air into the lung brionchioles Each bronchus branches repeatedly, giving rise to numerous bronchioles Each bronchiole ends in a cluster of alveoli Alveoli Gas exchange takes place through the walls of the alveoli Numerous alveoli are found in the lungs -> very large structure for gas exchange Inhalation/inspiration Diaphragm contracts and flattens Internal Intercostal muscles relax & external intercostal muscles contract The rib cage moves upwards and outwards Sternum moves up and forward Volume of thoracic cavity increases, lungs expands Decrease in air pressure in lungs Since atmospheric air pressure is now higher than the pressure within the lungs, air is forcedinto the lungs Exhalation/expiration Diaphragm relaxes and arches upwards Internal Intercostal muscles contract, external intercostal muscles relax Sternum moves down to its original position Rib cage moves downwards and inwards Volume of thoracic cavity decreases, lungs are compressed Increase in air pressure within lungs Pressure within the lungs is now higher than atmospheric pressure so air is forced out of your lungs Adaptations of the alveolus Thin film of moisture covers the inner wall of the alveolus ○ Allows oxygen to dissolve in it Large exposed surface area ○ Wall of the alveoli is only 1 cell thick ○ Short diffusion distance for carbon dioxide and oxygen ○ Higher rate of diffusion Walls of the alveoli are richly supplied with blood capillaries ○ Rapid flow of blood maintains the concentration gradient of gases How does gas exchange occur in the alveoli?  Blood entering the lungs (alveoli) has a lower concentration of oxygen and higher concentration of carbon dioxide than the atmospheric air entering the alveoli in the lungs A concentration gradient is set up between blood and alveolar air Oxygen dissolves into the thin film of moisture on the wall of the alveolus The dissolves oxygen then diffuses through the wall of the alveolus and the wall of the blood capillary into the red blood cells The oxygen combines with haemoglobin to form oxyhaemoglobin Carbon dioxide diffuses from the blood into the alveolar air How is the oxygen and carbon dioxide gradient between the alveolar air and blood? Continuous flow of blood through the blood capillaries Continuous breathing, which causes air in the lungs to be constantly refreshed Effect of tobacco smoke on human health Component Effects Nicotine Increases heart rate and blood pressure Increases the risk of blood clots in the arteries Increased risk of coronary heart disease Increased risk of arteries to narrow In a pregnant mother, narrowed arteries decrease the amount of food substances reaching the fetus, thereby affecting fetal development and may cause miscarriage Carbon monoxide Reduces the ability of blood to transport oxygen as carbon monoxide binds permanently with haemoglobin Thus, there will be less haemoglobin available to transport oxygen In a pregnant mother, less oxygen reaches the fetus through the placenta which may affect fetal development Increases the risk of coronary heart disease Tar Increases the risk of cancer in the lungs as tar can cause uncontrolled cell division Cancer is the uncontrolled division of cells producing outgrowths or lumps of tissue Increases the risk of chronic bronchitis Inflamed lining of the bronchus secretes excessive mucus Tar paralyses the cilia lining the air passages Dust particles trapped in the mucus lining cannot be removed Blocked airways -> persistent coughing -> lung infections Increases the risk of emphysema Breakdown of partition walls of alveoli Reduced surface area for gaseous exchange Reduced elasticity of lungs Lungs become inflated  Wheezing and severe breathlessness Mistakes Review Unit 1 Unit 2 Unit 3