I hope theses notes would serve you well for your upcoming mid year examinations !!! Good luck !!!
Enzymes
Enzymes are proteins that catalyse biochemical reactions. They remain unchanged after each reaction.
Specificity of enzymes All enzymes have a specific active site, which is complementary to only one substrate. Thus, only one type of molecule can bind to the enzyme to form an enzyme-substrate complex
Reusability of enzymes The enzymes are not part of the reaction that they catalyse. Thus, only a small amount of enzymes are needed to catalyse a large number of substrate molecules.
Effect of Temperature on Enzymatic reactions As the surrounding temperature increases, the kinetic energy of the molecules also increases. Thus, they collide more frequently and this increases the chance of them coming into contact with the enzymes active site. The enzymes catalyse substrate at a higher rate, specifically, for every 10deg Celsius increase in temperature, the rate of enzymatic reactions doubles. At the optimum temperature, the kinetic energy of the molecules are at the greatest and thus the rate of enzymatic reaction is at its greatest. When the temperature increases beyond the optimum temperature, the rate of enzymatic reactions decreases sharply. This is because the active site of the enzyme has changed its shape. The enzymes loses its complementarity with the substrate and the substrate molecules are not able to bind to the active site. Further increase in temperature will cause irreversible denaturation of the enzyme.
Effect of pH on Enzymatic reactions At the optimum pH, the rate of enzymatic reactions is the greatest. At extreme pH values above and below the optimum temperature, the ionic bonds in the enzyme are disrupted thus causing the denaturation of the enzyme. As a result, at these extreme pH levels, the rate of the enzymatic reactions is significantly reduced as the substrate molecules are not able to bind at the active site.
Effect of substrate concentration of Rate of Enzymatic Reactions The rate of enzymatic reactions increases until substrate concentration reaches X. The rate then remains constant as the enzyme molecules are saturated, as the substrate molecules have occupied all the available active sites of the enzymes.
Commercial applications of enzymes
Meat tenderiser - protease
Ice cream/milk - lactase which converts lactose into glucose and galactose
Cereals - cellulase
Agar from seaweed - cellulase
Stain removers in detergents - protease, amylase, lipase
Biopolishing of cotton fabric - cellulase
Transport of Substances
Diffusion
Net movement of atoms, ions or molecules from a region of higher concentration to a region of lower concentration, molecules move down concentration gradient, to form a homogenous environment.
Concentration gradient, temperature, and surface area through which diffusion occurs
Diffusion in Organisms Carbon dioxide and oxygen diffuses into AIR SPACES due to the lower concentration in the AIR SPACES
Partially permeable membrane - membrane that allows some molecules to pass through but not others.
Osmosis Net movement of water from a region of higher water potential to a region of lower water potential across a partially permeable membrane
Animal cells
Hypotonic ; Water flows in, lysis Isotonic ; No net movement of water, remains the same Hypertonic; The cell becomes flaccid, water flows out
Plant cells
Hypotonic: waterflows in ; turgid Isotonic; no net movement of water; remains the same Hypertonic; water flows in ;plasmolysis
Transport of Substances Diffusion Net movement of atoms, ions or molecules from a region of higher concentration to a region of lower concentration, molecules move down concentration gradient, to form a homogenous environment.
Concentration gradient, temperature, and surface area through which diffusion occurs
Diffusion in Organisms Carbon dioxide and oxygen diffuses into AIR SPACES due to the lower concentration in the AIR SPACES
Partially permeable membrane - membrane that allows some molecules to pass through but not others.
Osmosis Net movement of water from a region of higher water potential to a region of lower water potential across a partially permeable membrane
Active transport Method of transport that moves substances against the concentration gradient Requires energy in the form of ATP molecules In the root hair cells, Na+, Ca2+ is absorbed against the concentration gradient
Factors affecting diffusion/ osmosis Temperature-increase rate - more kinectic enerfy, move faster Concentration gradient-increase rate - moere moelecules cross over SA:V ratio-increase rate-more surface rae, shorter distance to travel
Plant growth Growth is the progressive development of an organism
Methods of measuring growth of the plant
- Height of the plant
- Size of the leaf
- Number of leaves
- Length of roots
- Fresh mass - mass of the live plant, may fluctuate as it takes into account the amount of water in the plant
- Dry mass - only takes into consideration the organic matter in the plant - most accurate measure
How to measure dry mass
- Remove and clean the plant
- Press the plant in between two pieces of absorbent paper
- Place the plant in the oven at 40deg
- Take plant mass. Back in oven.
- Repeat step 4 two times, until a consistent mass reading is achieved.
Factors affecting plant growth Light
- Quality/ Wavelength - quality of sunlight cannot be manipulated but quality of sunlight can
- Intensity - as intensity increases, the stomata will open at first, until the intensity causes high temperature that closes the stomata to prevent high rate of transpiration.
- Photoperiod - number of hours of light received by a plant per day.
Temperature
- Affects photosynthesis ( 18deg to 27deg )
- Respiration
- Transpiration The enzymes involved only works optimally at the optimum temperature.
Mineral salts Any element that functions in plant metabolism Macronutrients Micronutrients Nitrogen Copper Phosphorus Manganese Potassium Zinc Calcium Boron Magnesium Chlorine Sulfur Iron
Facilitation of mineral salts through active transport
Nutrient Functions Deficiency Symptoms Nitrogen Component of proteins and chlorophyll. Required for the growth of plants especially in younger plants - stunted growth, light green older leaves, chlorosis (older leaves turn yellow and die) Phosphorus Component of nucleic acid and phospholipids and Adenosine Triphosphate. Required for the flowering of plants. - Purplish veins in older leaves in older leaves, fewer seeds and fruits, stunted growth Potassium Activating enzymes, maintaining water-solute balance and effecting osmosis, required for root growth and fruit growth Reduced growth, mottled older leaves, burned leaf margins, burned leaf margins, weakened roots and stems.
Nitrogen can also be obtained in the form of ammonia as leguminous plants form a symbiotic relationship with Rhizobium bacteria. This is because they form a symbiotic relationship with the bacteria. Bacteria benefit by obtaining food and shelter while plant benefits by obtaining ammonia. The bacteria are nitrogen fixing, meaning the they convert atmospheric nitrogen to ammonia , which the plants use to make amino acids.
Seed structures and germination Testa - encloses the embryo and cotyledon, protects from injury and drying out Micropyle -a tiny opening in the testa through which water can enter can enter the seed through germination Embryo - consists of a radicle or plumule Cotyledon - contains food reserves, mainly starch, for the embryo after germination. Hilum - the scar on the seed that marked its original position on the fruit wall.
Protease, amylase and lipase enzymes become activated once dissolved in water.
Dormancy is a mechanism that allows for the prevention of germination in unfavourable surrounding ecological conditions, that would lower the chance of seed survival. It determines the timing of germination which contributing to successful seedling establishment and plant fitness.
Hypogeal germination Seed absorbs water and swells, then the radicle grows first and bursts through the testa. Radicle grows downwards into soil or growth medium. The epicotyl grows rapidly before the hypocotyl, puling the plumule out backwards to protect it; once the plumule is above the soil, the epicotyl straightens.
Epigeal germination Seed absorbs water and swells, then the radicle grows first and bursts through the testa. Radicle grows downwards into soil or growth medium. The hypocotyl grows rapidly, puling the cotyledons out above the soil before the growth of the epicotyl, which brings out the plumule from the cotyledons.
External conditions for Germination Water - absorbed through the dry testa and makes it permeable and soft, which allows for better gaseous exchange. Food materials in the cotyledon become soluble to be used by the embryo. Enzymes essential for growth and germination are able to start working.
Oxygen The oxygen enters the testa once it has been soaked. It is required for aerobic respiration, to release energy for growth. Energy is needed in the mobilisation of food reserves from the cotyledons to the growing zones and the synthesis of new protoplasm of the growing seedling.
Temperature Seeds germinate within a certain range of temperatures that vary considerably. Suitable temperature is important required so that enzymes can work optimally, to break down starch, proteins and lipids that can be used by plants.
Light Most plants are not influenced by light. Some plants need light to germinate while others cannot germinate in light (tomato, onion, lily)
Transport in plants
What is being transported? Phloem - sucrose and amino acids from the leaves to the other parts of the plant Xylem - water and dissolved mineral salts from the roots to the other parts of the plant.
Vascular bundle - xylem and phloem Arrangement (dicot) - root: xylem in a + shape with the phloem outside Arrangement (monocot) - stem: triangles pointing to the centre Stem - arranged in triangles pointing inward, in a circle Leaf - xylem on top, phloem on the bottom
Xylem Functions - transports water and dissolved mineral salts from roots, unidirectional flow, mechanical support due to lignified wall. Structure - many dead cells arranged in a long hollow tube, the crosswalks have been disintegrated - heavily lignified - consists of tracheids and vessels Tracheid -long slender cells connected by pits -shorter thiccer cells with completely perforated crosswalls.
Phloem - transports sucrose and amino acids Sieve tube elements joined to for, sieve tube plates, separated by sieve. They are living cells, they have a functional plasma membrane, with no major organelles such as mitochondria, nucleus and tonoplast
Companion cells Dense in organelles such as mitochondria and ER Provides ATP, proteins to the sieve tube elements
Root hair cells Functions to absorb water and mineral salts from the surroundings. Structure- long and thin hair-like structures on the root cell.
Adaptations of the root hair cell
- Long and thin - higher SA:V ratio, to increase rate of absorption
- Highly hypertonic with cell sap - maintain a low water potential in the cell to facilitate osmosis of water into RHC.
- Living cells - able to respire thus releasing energy for active transport of mineral salts into the RHC.
How the water moves up the xylem
- Root pressure - low potential of cell sap. Water entering RHC forces water up the xylem so that new water can come in, partially responsible
- Capillary action - caused by adhesion and surface tension - water adheres to the xylem vessels