♡ Topic 6_Plant structures and functions ♡

• Glucose produced in photosynthesis is stored in the plant's biomass as complex carbohydrate cellulose, which can be converted into other food, like lipids, or combined with nitrates to create amino acids.
• Starch is stored as an energy source.
• The word equation for photosynthesis is: Carbon dioxide + water -> glucose + oxygen.
• The symbol equation for photosynthesis is: 6CO2 +6H2O -> C6H12O6 +6O2.
• The three limiting factors for photosynthesis are CO2 concentration, light intensity and temperature.
• If the temperature is too low, the rate of photosynthesis will be slow as it is far from the enzyme's optimums.
• If the temperature is at the optimum, the rate of photosynthesis will be fast.
• If the temperature is above the optimum, the enzymes' active sites will denature.
• Light intensity affects the rate of photosynthesis, with a graph flattening out as light intensity increases, meaning that more light can be used in photosynthesis.
• As CO2 concentration increases, so does the rate of photosynthesis, until light intensity or temperature becomes the limiting factor, at which point, the rate will stop increasing.
• Root hair cells are adapted to their functions by absorbing water and mineral ions from the soil, having a large surface area for maximum absorption, and having lots of microchondria to provide the energy needed for active transport.
• Water is absorbed by root hair cells through osmosis.
• Mineral ions are absorbed by root hair cells through active transport.
• Phloem tubes transport food, mainly sucrose, produced in photosynthesis to all other parts of the plant for respiration.
• Translocation involves the movement of glucose (transported as sucrose) produced in photosynthesis to all other parts of the plant for respiration.
• The structure of phloem tubes is columns of elongated living cells, with small pores in the end walls to allow things to flow through.
• Xylem tubes transport water and minerals from the root to the rest of the plant, are strengthened with a material called lignin, and are part of the transpiration stream.
• The structure of xylem tubes is tubes made of dead cells joined end to end with no walls in between them.
• The transpiration stream is the movement of water from the roots through the xylem and out of the leaves.
• Gibberellins are plant hormones that stimulate seed germination, stem growth and flowering.
• Lots of seeds won't germinate without certain conditions.
• Shoots are positively gravitropic, growing upwards, away from gravity.
• Mustard cress seeds can be investigated in a petri dish lined with damp filter paper, and placed inside of a black card box, with a hole in one side only.
• Roots are negatively phototropic, growing away from light.
• Seeds can be treated with gibberellins to make them germinate at any time of year.
• Gibberellins make sure all seeds in a batch germinate at the same time.
• Gibberellins are another group of plant hormones and are important in initiating seed germination, stem growth and flowering.
• Auxins can be used in rooting powder which helps cuttings grow.
• When a shoot is growing sideways, in relation to auxins, more auxins accumulate on the lower side, causing cells on that side to grow more quickly, causing the shoot to bend upwards.
• If a root is exposed to light, in relation to auxins, more auxins accumulate on the shaded side, causing this side to grow more slowly, and the root to bend downwards into the ground.
• Fruit with seeds are usually only produced on flowering plants which aren't pollinated by insects.
• Roots are positively gravitropic, growing downwards, towards gravity.
• If a root is growing sideways, in relation to auxins, more auxins accumulate on the lower side, inhibiting growth there, causing the top side to grow more quickly and the root to bend downwards.
• Auxins can be used as selective weedkillers as weeds are broad leaved, but grasses and crops would have narrow leaves.
• Cells elongate more quickly on that side, so the shoot bends toward the light, allowing it to absorb more light for photosynthesis, allowing the plant to grow.
• Gibberellins can be used to make plants flower earlier than usual, or in different conditions.
• If giberellins (a type of plant hormones) are applied to unpollinated flowers, the fruit will grow, but the seeds won't.
• Gibberellins can also reduce flower formation to improve fruit quality.
• Ripening hormone called ethene can be added to the unripe picked fruit, meaning they will ripen on the way to shops and be perfect when they reach the shelves.
• The transpiration stream works by water being lost from the leaves through evaporation and diffusion, leading to a shortage of water in the leaves, which is replaced by more water being drawn up the plant through the xylem vessels.