Biology

1. Biology

2. Contents • Plant Processes • Leaf structure • Photosynthesis • Limiting Factors • Uses of Glucose • Plants and Water • Osmosis • Osmosis in Different Cells • Transpiration • Plant Growth and Fertilisers • Plant Senses and their Commercial Uses • Response to Water • Response to Gravity • Response to Light • Biomass, Farming and Decay • Biomass • Pyramid of Numbers • Pyramid of Biomass • Intensive Farming and Organic Farming • Pesticides • Fertilisers • Eutrophication • Decay and Food Preservation • Recycling of Carbon and Nitrogen • Key Words

3. Back to Contents Leaf structure Photosynthesis Limiting Factors Uses of Glucose Plants and Water Osmosis Osmosis in Different Cells Transpiration Plant Growth and Fertilisers Plant Senses and their Commercial Uses Response to Water Response to Gravity Response to Light Plant Processes

4. The Leaf Structure

5. The Leaf • It is the organ of photosynthesis • The waxy cuticle is a waterproof layer that cuts down the loss of water by evaporation • The epidermis allows sunlight to pass through to the palisade cells where most of photosynthesis takes place • It contains lots of chloroplasts which contains chlorophyll to absorb sunlight • The spongy layer contains rounded cells with lots of air spaces to allow carbon dioxide to circulate and reach the palisade cells • The leaf vein contains xylem and phloem tubes which supply water and glucose throughout the plant • At the bottom are stomata which open and close to let carbon dioxide in and water vapour and oxygen out • Guard cells surround the stomata and control their opening and closing • When there is a short supply of water the guard cells become flaccid and less curved. This closes the stomata to save on water • When there is a lot of water the guard cells become turgid and curved. The stomata are open and allows the water to escape • For maximum efficiency, the plant: • Leaves are flat with a large surface area to absorb as much sunlight as possible • They are thin to allow carbon dioxide to reach the inner cells easily • They have plenty of stomata in the lower skin • They have plenty of veins to support the leaf and carry substances around the plant

6. Leaves and Photosynthesis • A leaf has an upper and lower epidermis covered with a waxy cuticle • The spongy mesophyll and palisade cells contain chloroplasts • Guard cells surround the stomata • Leaves are adapted for efficient photosynthesis by having a large surface area, being thin and having veins • Photosynthesis occurs mainly in the leaves • Water enters the root hairs by osmosis • Carbon dioxide enters and oxygen leaves by diffusion through stomata • The leaf is very efficient in photosynthesising because it has a large internal surface area, internal air spaces and many chloroplasts in the palisade layer • There are three main limiting factors that affect the rate of photosynthesis. They are: • Light • Carbon dioxide • Temperature

7. Limiting Factors 45°C

8. Uses of Glucose • Some glucose is used in respiration to obtain energy • Other uses include converting it to: • Insoluble starch stored in the roots, particularly in the winter. In this form it does not cause too much water to move into the cells by osmosis, as it doesn’t contribute to the concentration inside the cells • Cellulose, needed for cell walls • Lipids and oils are formed from glucose and stored in seeds • Glucose can also be combined with other substances, such as nitrates obtained from the oil and turned into proteins

9. Plants and Water • Plant cells are supported by their cell walls and turgor pressure in the cell sap • Water enters the root hairs by osmosis • Osmosis is the movement of water from a high concentration to a low concentration through semi-permeable membrane • A semi-permeable membrane only allows the movement of small molecules • Water moves both in and out of the root to try to even the concentrations. Therefore we use the net movement of water • Osmosis is a type of diffusion • A plant must balance its water uptake and water loss • Water is needed for photosynthesis, cooling and transport • A leaf is adapted to reduce water loss • Leaves lose water because a leaf is adapted for photosynthesis

10. Osmosis • Root hairs take in water by osmosis • Water moves along the cells of the root and up the xylem to the leaf • All the time the water is moving to areas of lower water concentration • Osmosis makes plant cells swell up • The water moves into the plant cell vacuole and pushes against the cell wall making it turgid • It is useful as it gives the stem support • When there is little water the cells become flaccid as water has moved out of the cell • If a lot of water leaves the cell, the cytoplasm started to peel away from the cell wall which is called plasmolysis • The cell will behave differently in an animal cell because there is no cell wall to prevent the cell from bursting (haemolysis)

11. In a Plant In an Animal Osmosis in Different Cells Normal Too Little Water Too Much Water

12. Transpiration • Water loss from a plant is called transpiration • The water evaporates and exits the leaves by diffusion • Water travels from the roots, through the stem to the leaves in xylem cells • Dissolved food travels downwards in phloem cells • The rate of transpiration is speeded up by a higher temperature, more wind, a low humidity and more light • More light will increase the transpiration rate because the stomata will be open • A higher temperature will increase the transpiration rate by increasing the diffusion rate • A low humidity will allow more water vapour to diffuse out of the leaves • Xylem cells are dead because they have extra lignin thickening • The flow of water up the xylem to the leaves is called the transpiration stream • The transpiration stream also draws minerals into the plant as well as water • As water is lost, the transpiration stream replaces it so there is a constant flow

13. Back to Contents Fertilisers and Plant Growth • Plants need minerals in fertilisers such as nitrates, phosphates, potassium and magnesium compounds • Minerals are needed only in small quantities • Nitrates are needed to make proteins for growth • Phosphates are needed for root growth • Potassium is needed for flower formation • Magnesium is needed to make chlorophyll • If minerals are missing from the soil water, the plant shows that it is mineral-deficient • Minerals are taken up from the soil water by active transport • Minerals are taken up against a concentration gradient • Active transport uses energy • An NPK fertiliser contains nitrogen (N), phosphorus (P) and potassium (K)

14. Back to Contents Plant Senses Commercial Uses • Plants respond to their surroundings to give them a better chance of survival • Plant responses are called tropisms and are controlled by a hormone • Plants respond to light, gravity and water • Remember: unequal distribution of auxin speeds up growth in shoots and slows down growth in roots • Growing Cuttings • Rooting powder contains synthetic auxins • A cutting is taken from a plant and dipped in this powder. This stimulates the roots to grow quickly and enables gardeners to grow lots of exact copies of a particular plant • Killing Weeds • Synthetic auxins are used as selective weed-killers • They only affect the broad-leaved weeds; narrow-leaved grasses and cereals are not affected • They kill the weed by making the weed grow to quickly • Seedless Fruits • Synthetic auxins are sprayed on unpollinated flowers • Fruits form without fertilisation and thus form without pips • Early Ripening • Plant hormones can also be used to ripen fruit in transport Plant Senses and Commercial Uses

15. Back to Contents Response to Water Response to Gravity • A plant’s response to water is called hydrotropism • Roots always grow to a certain extent towards water, even if it means ignoring the pull of gravity and growing sideways • An uneven amount of moisture will cause more auxin to appear on the side with more water • This inhibits the growth of cells on this side • The root cells on the outside will grow quicker and will bend towards the moisture • A plant’s response to gravity is called geotropism • Even if you plant a seed the wrong way up, the shoot always grows up, away from gravity and the root grows down towards gravity • If a plant is put on its side, auxin gathers on the lower half of the shoot and root • Auxin slows down the growth of root cells, so the root curves downwards • Auxin speeds up the growth of the shoot cells so the shoot curves up Responses to Water and Gravity

16. Back to Contents Response to Light • A plant’s response to light is called phototropism • Plants need light for photosynthesis and thus grow towards the light • Normally light shines from above. Auxin is spread evenly and the shoot grows upwards • If light comes from one side, auxin accumulates down the shaded side. Auxin makes these cells grow faster • The result is that the shoot bends towards the light

17. Back to Contents Biomass Pyramid of Numbers Pyramid of Biomass Intensive Farming and Organic Farming Pesticides Fertilisers Eutrophication Decay and Food Preservation Recycling of Carbon Recycling of Nitrogen Biomass, Farming and Decay

18. Back to Contents Biomass • Energy enters food chains in photosynthesis • Plants are producers because they produce food • Animals are consumers • A pyramid of numbers show the number of organisms in each link (trophic level) in a food chain • A pyramid of biomass shows the mass of living material in each link (trophic level) in a food chain • Energy is transferred along a food chain or food web • Some energy is transferred into less useful forms such as hear or body waste • Biomass fuels are wood (by burning), alcohol (by fermentation) and biogas (from decay) • Biomass fuels are renewable, produce less pollution and are energy self-reliant

19. Back to Contents Pyramids of Numbers • A pyramid of numbers tells us how many organisms are involved at each stage in the food chain • At each trophic level the number of organisms get less • However, sometimes a pyramid of numbers doesn’t look like a pyramid at all because it doesn’t take into account the size of the organisms • E.g. There are many fleas on a single fox which would make the pyramid ‘top heavy’

20. Back to Contents Pyramids of Biomass • A biomass pyramid takes into account the size of an organism at each level unlike the pyramid of numbers • It looks at the mass of the organism • You can take the information from the pyramid of numbers and multiply it by the organism’s mass which will achieve the pyramid shape again

21. Back to Contents Intensive and Organic Farming • Intensive farming uses pesticides (insecticide and fungicide) to kill pests and herbicides to kill weeds • Intensive farming produces more food but also causes problems such as pesticides accumulation in food chains • Fish farming, glasshouses, hydroponics and battery farming are all examples of intensive farming • Organic farming does not use artificial fertilisers, herbicides or pesticides • Organic farming uses animal manure, crop rotation, hand-weeding and biological control of pests • Intensive farming improves the efficiency of energy transfer in food chains • Hydroponics gives better control of fertilisers and diseases

22. Back to Contents Intensive Farming • Intensive farming can produce more food because it is designed to provide more food for the given land • Many people regard intensive farming of animals as cruel • In order to produce more food from the land, fertilisers and pesticides are needed

23. Back to Contents Pesticides • Pesticides are used to kill insects that damage crops • They also kill harmless insects, then insect-eating birds have a shortage of food • The pesticides can get washed into rivers and lake which can then get into our food chains • This was the case in the 60s when a pesticide, DDT, got into the food chain and threatened populations of animals

24. Back to Contents Fertilisers • Plants need nutrients from the soil to grow • Artificial fertilisers are used to replace the nutrients in the soil because there isn’t enough because of intensive farming • Fertilisers enable farmers to crop more crops in a smaller space. • Less countryside will be lost for farming but eutrophication is caused because of fertilisers

25. Back to Contents Eutrophication • If too much fertiliser is used and it rains, it goes into rivers and lakes • The water plants grow quicker as a result of this and they quickly cover the surface of the water • There is then more competition for light and some plants die • Microbes break down the dead plants and use the oxygen for respiration • The amount of oxygen in the water is then reduced and animals die through suffocation • Untreated sewage can also cause eutrophication

26. Back to Contents Organic Farming • People need to limit their needs • Intensive farming produces quality food and enough to supply people’s needs in Europe but has its problems – alternative is organic farming • Organic farming produces less food per area of land but is kinder to the environment • Organic farming uses manure as a fertiliser and has land for wild plants and animals to flourish. • Biological control of pests are also used where animals eat the pests, it’s not as effective but it isn’t harmful Back to Contents

27. Back to Contents Decay and Food Preservation • Decomposers such as fungi and bacteria cause decay • Decay breaks down sewage and compost • Decay is affected by temperature and the amount of oxygen and water • Detritivores are animals that feed on dead and decaying material • Earthworms, maggots and woodlice are Detritivores • Saprophytes are plants that live on dead and decaying material • Food can be preserved by stopping or reducing decay • Food preservation methods include canning, freezing, drying and adding salt, sugar or vinegar

28. Back to Contents Recycling of Nitrogen and Carbon • When plants and animals die, their chemicals, such as nitrogen and carbon, are recycled • Plants remove carbon fro the air by photosynthesis • Respiration and the burning of fossil fuels releases carbon in the form of carbon dioxide • Carbon is recycled through marine shells, limestone and eventual weathering • There is 78% nitrogen in the atmosphere but it is unreactive • Plants take in nitrogen as nitrates • Dead bodies decay, releasing nitrates • Decomposers convert proteins and urea into ammonia • Ammonia is converted into nitrates by nitrifying bacteria • Some nitrates are converted into nitrogen by denitrifying bacteria • Nitrogen-fixing bacteria in the soil and root nodules fix atmospheric nitrogen • (This is further explained on the next few slides...)

29. Back to Contents The Carbon Cycle Key Takes out of Atmosphere Puts in Atmosphere Does Neither The atmosphere Photosynthesis Feeding Death and Decay Respiration Burning and Combustion Decomposers Death but no decay Fossil Fuels

30. Added Notes: Decomposition Decomposers are bacteria and fungi which break down dead material They help recycle carbon into the atmosphere and recycle nutrients into the soil Plants use this nutrients dissolved in water during photosynthesis. Animals eat plants, and both animals and plants die, making the cycle start from the beginning again Decomposition happens everywhere in nature, in compost heaps and even sewage works The perfect conditions are: Warm Moist Plenty of oxygen The Carbon Cycle in Detail Back to Contents

31. Back to Contents The Nitrogen Cycle

32. Back to Contents The Nitrogen Cycle

33. The atmosphere contains 78% nitrogen gas Nitrogen is needed to make protein Plants and animals cannot use nitrogen as a gas – it has to be converted into nitrates Animals get protein by eating plants which plants make from nitrates It is a continuous cycle There are four ways that nitrogen is converted into nitrates and only two ways that nitrogen is taken out of the soil There are three different types of bacteria involved in this cycle: Nitrifying bacteria Nitrogen-fixing bacteria Denitrifying bacteria Back to Contents The Nitrogen CycleAdded Notes 9 8 Proteins in Plants 6 Death and Decay Proteins in Animals 10 7 11 12 5 Fertilisers 13 1 Nitrogen in the air 14 2 Soil Nitrates 3 4

34. Back to Contents The Carbon Cycle The Nitrogen Cycle • Photosynthesis • Respiration • Combustion • Carbon • Fossil fuels • Decomposers/decomposition • Nutrients • Warmth • Moisture • Oxygen • Lightening • Nitrates • Nitrogen • Nitrogen-fixing bacteria • Root nodules • Protein • Detritivores • Decomposers • Nitrifying bacteria • Leaching • Denitrifying bacteria Key/ Scientific Words

35. Back to Contents More Key/ Scientific Words... • Xylem • Phloem • Transpiration • Starch • Vascular bundle • Nitrates • Phosphates • Potassium • Magnesium • Iron • Osmosis • Large surface area • Transpiration stream • Cuticle • Stomata • Guard cells • Light • Temperature • Humidity • Flaccid • Turgid • Carbon dioxide • Water • Glucose • Oxygen • Photosynthesis • Cellulose • Lipids • Proteins • Enzymes • Epidermis • Palisade cells • Leaf vein • Spongy layer/ mesophyll • Chloroplasts • Chlorophyll • Active transport • Diffusion • Semi-permeable • Net movement • Plasmolysis • Haemolysis • Limiting factors • Lignin • Concentration gradient • Biomass • Pyramid of numbers • Trophic level • Biogas • Fermentation • Pesticides • Intensive farming • Organic farming • Fertilisers • Eutrophication • Hydroponics • Decomposers • Detritivores • Saprophytes • Tropisms • Auxin • Hydrotropism • Geotropism • Phototropism