Biology Module 4 Notes

B4A – Who planted that there? •Leaves have a key role for photosynthesis •This uses the green chemical chlorophyll •All green plants have this chemical, but some have other chemicals that change pigmentation •Venus fly traps have special leaves that trap flies •Stinging nettles have hairs that inject poison •Photosynthesis is carried out by some bacteria •It changes sunlight into energy in the form of glucose •Water + Carbon Dioxide → Oxygen + Glucose •The structure of a leaf ◦Cuticle – Waxy layer that prevents water entering the top of the leaf ◦Upper Epidermis – Has no chloroplasts and allows light to reach the palisade layer. ◦Palisade Mesophyll – This layer contains most of the chloroplasts are and is where most photosynthesis takes place ◦Spongy Mesophyll – Allows gases to diffuse between the stomata and the photosynthesising cells ◦Stomata – Are openings controlled by the guard cells ◦Lower Epidermis – None of these cells, other than the guard cells, have chloroplasts •Evolutions of the leaf ◦Large surface area to absorb light energy ◦This to lower distance gas must travel ◦Vein networks carry water in and glucose out ◦Stomata to allow diffusion ◦Chlorophyll for photosynthesis ◦Air spaces for a large internal area-to-volume ratio B4B – Water, Water Everywhere •Osmosis is how water is taken up by the plant •Plants need water to prevent wilting •Water moves in and out of plant cells through the cell wall and membrane •When the vacuole of the cell is full of liquid and the turgor pressure is high then the cell is turgid •If a cell is losing more water than it gains and the turgor pressure falls, the cell is flaccid •Plasmolysis - If a cell loses so much water that the membrane detaches from the cell wall •Osmosis is a special type of diffusion ◦The cell wall is permeable ◦The cell membrane is semi-permeable so only small molecules can diffuse through ◦Osmosis is the movement of water from an area of high water concentration to an area of high water concentration across a partially permeable membrane ◦If a plant cell is placed in water, it will stop swelling because the water concentration inside and outside of the cell is equal ◦Animal cells also use osmosis ▪Lysis – An animal cell only has a permeable cell membrane, so if the cell takes to much water it will burst ▪Crenation – Lack of water in a concentrated solution for a cell ◦Water lost through stoma is called transpiration ◦Root hairs increase surface are which increases the uptake of water ◦The flow of water to leaves helps by ▪Helping to cool the plant ▪Providing the leaves with water for photosynthesis ▪Makes all cells stay turgid ▪Brings up minerals

◦How is water loss controlled? ▪Waxy cuticle to prevent loss from the top of the leaves by evaporation ▪Guard cells that close when light and water is low because the cells aren't turgid and don't bend B4C – Transport in plants •Sugar and Water are transported in different cells in plants •The two transport tissues are called xylem and phloem •Xylem is always on the inner side of a dicotyledonous plants leaf, stem and root •Xylem transports water and dissolved minerals from the roots to the leaves where it is lost in transpiration •Phloem transports sugars, unlike Xylem, food can go up or down the stem ◦It can move to the tip of the shoots for growth ◦It can move to the roots for storage •This movement is called translocation •Phloem and Xylem are held together in collections called vascular bundles •Specialisation of Xylem ◦Thin tubes called “Vessels” have hollow lumen ◦They are made from dead cells ◦Hollow vessels allows water to easily pass through ◦Thick cell walls prevent collapse and support the plant •Specialisation of Phloem ◦Column of living cells ◦Cells have holes in the end walls to allow the passing of food •When the transpiration rate is high, suction is created which pulls more up water up through the xylem •Transpiration rate increases ◦When the temperature increases – Faster Evaporation ◦When light levels increase – Causes stomata to open ◦When its windy – Water vapour is blown away ◦When its dry and not humid – Air hold less water molecules increasing the diffusion rate B4D – Plants need minerals too •Plants need minerals to grow properly •Plants get mineral from the soil and need them for correct growth •Minerals are absorbed by being dissolved in water and being taken in up the roots •Some plants use fungi to collect nutrients and insert them into the roots •Some plants are carnivorous and trap insects to extract their minerals •Plants need minerals to change sugars into other substances ◦Magnesium from Magnesium compounds – Chlorophyll for photosynthesis ◦Nitrogen from nitrates – Amino acids for making proteins which are needed for cell growth ◦Phosphorus from phosphates – DNA and cell membranes needed to make new cells for growth and respiration ◦Potassium from potassium compounds – Compounds needed to help enzymes in photosynthesis •Without certain minerals, a plant will gain a deficiency, different mineral deficiencies are visible in different ways ◦Magnesium – Yellow leaves ◦Nitrate – Poor growth and yellow leaves ◦Potassium – Poor flower and fruit growth and discoloured leaves ◦Phosphate – Poor root growth and discoloured leaves •Farmers may add fertilisers to the soil to increase crop growth

◦Plants need different levels of each mineral ◦In an NPK soil, the levels of each mineral are shown on the front •Minerals are absorbed through the roots as they are dissolved in the water at low concentration •The concentration on the root hairs is higher and they have to be taken by active transport •This moves substances are moved against the concentration gradient (low to high) which needs energy from respiration ◦Farmers try to ensure water is not waterlogged as this reduces oxygen content in the soil, needed for respiration B4E – Energy flow •Plants trap sunlight energy and convert it into products useful to us •Some foods take more energy to to extract their energy such as celery •Energy from plants is used both for energy and fuel •The first organism in a food chain is a producer, all others are consumers •A food chain can be demonstrated as a pyramid of numbers ◦Each stage is called a trophic level •Since a pyramid of numbers does not account for size of each organism, a pyramid of biomass is used (mass of living material in each organism) •Energy flow ◦Energy enters the food chain through sunlight ◦It is stored as glucose ◦This energy is then passed through the food chain ◦Energy is lost by ▪Respiration ▪Egestion (Bum Fudge) ▪Heat ◦The larger the difference between two groups on a pyramid of biomass, the lower the efficiency of energy transfer •Uses for energy from biomass ◦Burn wood from fast growing trees ◦Produce alcohol by using yeast to ferment it ◦Produce biogas by using bacteria •Biofuels are good because carbon dioxide levels in the air remain constant B4F – Farming •Intensive farming is when machinery and chemicals are used to produce as much food as possible from land •Battery farming involves keeping animals indoors and keeping movement restricted so they lose less energy through heat •Intensive farming improves energy transfer efficiency ◦Pesticides are used to improve biomass ◦Herbicides are used to reduce competition so crops gain more sunlight ◦Certain pesticides do not break down in the body and can kill •Some farmers do intensive farming in glasshouses to protect the plants •Some farmers use hydroponics – growing the plants in water or artificial soil •Advantages of hydroponics ◦Control of mineral levels ◦Control disease by adding pesticides to the water, ensuring it gets to every plant •Disadvantages of hydroponics

◦There is no deep soil for support ◦Fertiliser and minerals must be added to the water •Organic Farming – Growing plants without artificial fertilisers, herbicides or pesticides •Alternative methods ◦Animals manure and compost can be used as fertiliser ◦Nitrogen fixing crops can be grown ◦Crop rotation can be used so pests cannot build up in the said ◦Crops can be hand weeded ◦Farmers can vary seed planting times ◦This methods are more labour intensive ◦This is only successful if consumers are willing to pay more for their food •Pest control ◦Using organisms to control pests is called biological control ▪Usually these are predators that eat the pests ▪An issue with this is that it may damage the food web and other animals may die out ▪Another issue is that the control organisms may become pests themselves B4G – Decay •Plants and animals are made from organic material, when this breaks down, it is called decay •Organisms that break down dead organic material are called decomposers •They allow chemical elements to be recycled •The two main groups of decomposers are bacteria and fungi ◦They release enzymes to partially digest the chemicals and then take them up ◦This feeding is called saprophytic nutrition ◦The bacteria and fungi are called saprophytes •Another group are animals that feed on pieces of dead and decaying material ◦These pieces are called detritus ◦The animals are called detritivores ◦Detritivores increase decay by breaking up material so it has a greater surface area •Rate of Decay is increased when there is ◦High oxygen levels for the microbes to respire ◦Water for substances to dissolve and for the chemical reactions of respirations to occur ◦Micro-organisms to break down the material ◦Warm temperature to keep respiration and growth of the microbes optimised •Food preservation is preventing food from decay ◦Canning – food is heated to boiling point and then canned, this kills micro-organisms and prevents water and oxygen entering ◦Cooling – Food is kept in refrigerators which slows down the growth and respiration of microorganisms ◦Drying – Dry air is past over the food, preventing respiration of the micro-organisms ◦Freezing – Food is keep well below freezing so micro-organisms cannot respire or reproduce because chemical reactions are slowed ◦Adding salt or sugar – this draws water away from the micro-organisms ◦Adding Vinegar – Prevents the enzymes from working because the vinegar is to acidic ◦Food can have chemicals added ▪People claim they taste funny or have side-effects B4H – Recycling •Recycling chemicals is important for us to gain carbon, nitrogen and oxygen as well as other elements

•Fritz Haber invented a process to combine nitrogen with hydrogen to make ammonia, a fertiliser •Carbon is the base for all living organisms •The main source of carbon is carbon dioxide in the air and it enters living organisms when plants photosynthesis •Carbon can be found in the bottom of the sea ◦Some animals make their shells out of carbonates ◦This is compressed into limestone rock ◦It can be worn away by weathering and joins the carbon cycle •The Carbon cycle ◦Animals release carbon dioxide in respirations ◦Plants use it in photosynthesis ◦Animals receive it through feeding ◦Animals die and their carbon dioxide is released by decomposers ◦Animal remains are burned for fuel and carbon dioxide is released •The air is 78% nitrogen •The Nitrogen cycle ◦Plants absorb nitrates through their roots ◦This is transferred in feeding ◦When animals die, their nitrogen is transferred by decomposers in to ammonium compounds ◦Nitrifying bacteria oxidise the compounds into nitrates ◦Some nitrogen is returned to the air by denitrifying bacteria ◦Some nitrogen from the air is changed to nitrates by nitrogen fixing bacteria