B4a Who Planted That There

B4a Who Planted That There? / ·  The green colour of a leaf is caused by the pigment chlorophyll
·  The leaf has veins running through it to bring water and minerals to the leaf- they also take away substances that the leaves make like sucrose and deliver them to other parts of the plant
·  The epidermis covers the leaf and protect the cells under them- they make a waxy, waterproof layer called the cuticle that stops the leaf drying out
·  The palisade cells are tall and thin and are stacked close together. To increase photosynthesis. They contain a lot of chloroplasts containing the chemical chlorophyll
·  The spongy layer contains less chloroplasts and has air spaces for gas exchange
·  The veins have xylem vessels for water and phloem tubes for sucrose
·  The gaps of holes in the bottom of the leaf are called stomata and allow air and water to move in and out of the leaf. Surrounding each stoma (gap) is a pair of guard cells which open or close the stoma
B4a Who Planted That There / ·  The palisade cells need carbon dioxide, water and light to photosynthesise and make glucose for respiration
·  Most leaves are broad to give a large surface area for sunlight
·  Leaves are usually thin so that sunlight can reach most of the cells in the mesophyll- also most cells are never far away from the air so carbon dioxide can diffuse in and oxygen made by photosynthesis can get out
·  Chloroplasts contain chlorophyll which absorbs sunlight
·  There are veins which transport water and sucrose, and also support the leaf and hold it flat for sunlight
·  Stomata on the underside of the leaf allow gas exchange to take place
·  The Epidermis is transparent so light can get through to the palisade cells
·  The palisade layer is near the top where it can get most light
·  The air spaces allow diffusion
·  The internal surface area is large compared to its volume to increase the rate of diffusion and therefore increase the rate of photosynthesis
B4b Water, Water Everywhere / ·  Water enters cells by osmosis
·  Particles of water move randomly, if there are more water molecules on one side of the membrane that the other, they will move from the high concentration (more water molecules) to a low concentration (less water molecules)
·  On the left of the diagram there are less solute (sugar) molecules and more water molecules (a high concentration of water). On the right, there are more solute molecules and less water molecules (a low concentration of water). So water moves from the left to the right, as there are more of them on the left.
·  We say that the water molecules have moved down their concentration gradient from a high water concentration to a low water concentration.
·  The water in the diagram is moving across a partially permeable membrane, which is a membrane with small holes that lets molecules of a certain size through (like water)
·  The cell membrane of body and plant cells is partially permeable too, so water can enter and leave them by osmosis
B4b Water, Water Everywhere / ·  The cytoplasm is just like a solution- many different substances dissolved in water.
·  There is a concentration gradient for water outside and inside the cell
·  If the plant cell is put into pure water, there are more water molecules outside than in, so overall, water moves into the cell by osmosis and the cell swells up. It doesn’t burst because it has a cell wall.
·  A plant cell that is swollen with water is said to be turgid
·  If a plant cell is put into a solution with a low number of water molecules and lots of solute like sugar etc. water will move out of the cell and the cell’s cytoplasm will shrink.
·  A plant cell with a shrunken cytoplasm is first called flaccid, then after more shrinking is said to be plasmolysed
·  The same process happens in a body cell (like a blood cell) but because animal cells have no cell wall, when water moves into them, instead of going turgid, they burst- this is called lysis. Also, if water moves out of them, they shrink, which is called crenation.
·  Having turgid cells help a plant, especially in the stem, as cells swollen with water (turgid) help to make the stem strong, plants rely on this turgor pressure to keep them upright. If the cells go flaccid, the plant will lean over to the side and sag.
·  Root hair cells on the plants roots help the plant cells to stay filled with water by providing a large surface area in the soil
B4c Transport In Plants / ·  After the water gets into the plants through the root hairs by osmosis, it moves into a dead, empty cell called a xylem vessel.
·  These cells are long and narrow and join up with each other end to end. They are also completely empty like drainpipes all linked together.
·  They stretch all the way from the roots, up the stem into the leaves and flowers
·  Xylem is made of cellulose and a strong material called lignin
·  You must remember that phloem is on the outer ring and xylem is on the inside like the drawing opposite as you may have to label the xylem and phloem in the exam
·  Phloem is made of columns of long cells stacked end to end to make long tubes, however they are alive and they don’t have lignin in their cell walls
·  Phloem transports sugars and other substances that are made during photosynthesis. This is called translocation.
·  Phloem and xylem tubes are often found together in what is known as vascular bundles
B4c Transport In Plants / ·  Water moves up through a plant because it is continually evaporating from its leaves- this is called transpiration
·  As water is lost from the leaves, they end up with a low water concentration inside them- this causes water to flow into them from the nearby xylem vessels, by osmosis.
·  Xylem vessels are a bit like a straw, and as water is moved from the top of the vessel to the leaves, it is replaced from water lower down the xylem vessel, which is in turn replaced by water from the roots.
·  Temperature speeds up the rate of transpiration as water is quickly evaporated from the leaf cells. Diffusion also happens faster.
·  The more light there is, the more photosynthesis a plant does, so its stomata are open to get carbon dioxide in, however water is lost through these stomata, which also speeds up transpiration
·  On a windy day, water is quickly removed after it has moved out of the leaf, so this speeds up transpiration.
·  The more humid it is, the less transpiration, as on a humid day, there is already lots of water in the air, so there is not much space for more water from the leaf. Transpiration slows down on a humid day.
B4c Transport In Plants / ·  An apparatus called a photometer measures the rate of transpiration
·  You can watch the meniscus (the water level) move along the calibrated pipette towards the plant.
·  The faster the plant is transpiring, the faster the water moves along
·  By refilling the water, you can change different things like how much light the plant gets, or the temperature the plant s kept at. Then record the results and find out how different variables affect the rate of transpiration
·  Transpiration helps the plant, by cooling it (a bit like sweating) so that chemical reactions inside it can happen at the correct rate.
·  Transpiration also helps by providing water for photosynthesis and minerals dissolved in the water to keep the plant healthy.
·  Plants also have ways of cutting down the rate of transpiration if they don’t want a lot of water loss e.g. desert plants.
·  They have a waxy cuticle on top of their leaves that is waterproof
·  Most of the stomata (small openings) are on the bottom of the leaf so they don’t get too much sunlight shining directly onto it
·  The stomata can be closed by the guard cells that change shape depending on the amount of water in them
·  Desert plants have stomata that are sunken in grooves so that the wind can’t reach them, some desert plants also have tightly rolled up leaves so that evaporation is reduced
B4d Plants Need Minerals Too / ·  Plants need minerals to make structures and chemicals in their bodies, which they absorb from the soil through their roots
·  Nitrate is used to make proteins which are made of long chains of amino acids with at least on nitrogen atom. They can’t use nitrogen from the air, but normally use nitrates NO3- but can also use ammonium ions NH4+ (an ion is just an atom with more or less electrons than normal)
·  Phosphate is needed to make DNA. It makes up the backbone of the DNA double helix molecule. Phosphorous is also used to make cell membranes.
·  Potassium ions make enzymes for photosynthesis to work properly. Respiration must have potassium ions available.
·  Magnesium is present in chlorophyll, and it is essential for the chlorophyll to absorb light energy for photosynthesis
B4d Plants Need Minerals Too / ·  Farmers can add fertilisers to the soil to add minerals to make their plants grow better
·  Fertilisers contain nitrogen, phosphate and potassium and are called NPK fertilisers
·  Many farmers use GPS (global positioning system) to make a map of their field to help them to find out where fertiliser is needed- they sample the soil and a computer tells them if the soil needs minerals to be added
·  Plants have symptoms if they have grown without certain minerals:
·  No nitrogen = small, pale plant with old yellow leaves. No Phosphorous = dull and discoloured leaves. No Magnesium= yellow and brown leaves. No Potassium= discoloured leaves and bad flower and fruit growth.
·  If the concentration of minerals is high in the soil, it will diffuse into the roots from a high concentration to a low concentration
·  If the concentration of minerals is low, the roots have to use special pumps in their cell membranes to push minerals from a low concentration into their cells. This is called active transport, and it uses energy
B4e Energy Flow / ·  Food chains show how energy is transferred from one organism to another
·  The arrows show the direction of energy flow
·  We can also add the energy in sunlight to the chain- then we call it an energy chain
·  In this chain, the grass is the producer, as it produces food by photosynthesis- they are always at the beginning of every food chain
·  The rabbit and fox are consumers- they consume the food made by the producers. All animals are consumers.
·  Pyramids of number show the number of organisms in a food chain or in a habitat
·  Each level in a pyramid of number is called a trophic level. The producers are on the first trophic level, the primary consumers on the second and the secondary consumers on the third
·  The mass (amount) of living material is called biomass
·  A pyramid of biomass shows the mass, not the number of organisms in the food chain
B4e Energy Flow / ·  Every time energy is transferred from one kind to another, some is wasted.
·  Energy can be wasted through egestion (energy lost in faeces- poo!), and also by respiration for things like moving around, or heat loss.
·  By the time the energy gets to the next consumer, there is only a small proportion left.
·  The efficiency of energy transfer can be calculated using the example on the left. 3056kJ of energy enters the cow. 1022kJ and 1909kJ is lost through waste and heat, so there is only 1045kJ of energy left. 3056kJ – (1022kJ + 1909kJ) = 1045 kJ
·  1045kJ ÷ 3056kJ = 0.34
·  0.34 × 100 = 34% So the efficiency of the cow is 34%
·  the calculation can be summarised by the sum: efficiency of energy transfer = energy transferred to next level ÷ energy in the previous level x 100
B4e Energy Flow / ·  Anything made from living organisms is called biomass, like plant material or manure. It is renewable energy, so can always be made.
·  A small amount of biomass is used in power stations to generate electricity (it’s burned to turn water to steam that drives a generator)
·  Wood can be harvested by a process called coppicing (cutting them then letting them re-grow)
·  The transport costs are high, and it is carbon neutral
·  Carbon neutral means that the carbon dioxide that the wood gives out when it is burned is equal to the carbon dioxide that it took in, so it is not causing carbon dioxide to be released into the atmosphere contributing to global warming
·  Another advantage of using biomass is that we can keep growing our own
·  Biomass can be used to make biogas by fermentation with bacteria and yeast in a digester. In china, people have their own biogas digesters next to their house for their waste and use the biogas to heat their house.
·  A type of alcohol called bioethanol can be made by yeast fermenting biomass. It can fuel cars and is used in Brazil at the moment.
B4f Farming / ·  Farming involves growing crops and keeping animals to produce food
·  To get high yields from crops or farm animals you have to have high inputs like chemical fertilisers to help crops grow well.
·  Weed killers and herbicides kill other plants in the field so that only one type of crop can grow and use the soils nutrients to stop competition. A selective weed killer kills the weeds, but not the crops.
·  Pesticides and fungicides kill diseases like fungus that can infect the crop.