What is the word and symbol equation for photosynthesis?
Carbon dioxide + water –> Glucose + oxygen
6CO2 + 6H2O –> C6H12O6 + 6O2
What is sugar from photosynthesis used for?
Making energy by respiration in cells
Making cellulose for building cell walls
Combining with nitrates to make protein
Making oils for storage in seeds
Why are plants important?
They create food, medicine, oxygen and fuel
How does light intensity affect the rate of photosynthesis?
As the light level increases, the rate of photosynthesis increases steadily (directly proportional) up go a point, where temperature or CO2 becomes the limiting factor.
How do you calculate light intensity?
Light intensity is proportional to 1/distance^2
How does carbon dioxide concentration affect the rate of photosynthesis?
Increasing CO2 concentration increases the rate of photosynthesis to a point. After this the graph flattens out as CO2 is no longer the limiting factor.
What is the structure of a leaf?
Waxy cuticle - to keep water in the lead
Epidermis - to protect other cells and to give the leaf structure
Palisade cell - contain chloroplasts for photosynthesis
Spongy mesophyll tissue - have gaps between them to let gases move through
Stomata - gaps between guard cells to let gases move in and out of the leaf
Guard cells - can open and close the stomata to allow or prevent gas exchange.
What are the three limiting factors of photosynthesis?
How do plants transport substances?
Water and solutes come from the soil and are absorbed through the roots by osmosis and active transport. Water and solutes then move through the roots until they reach the xylem. They then move up the xylem vessels through the stem to the leaves by transpiration. Water then evaporates through the stomata, known as transpiration.
Sugars, made from photosynthesis, move through the phloem to growing parts of the plant and storage tissues.
What are xylem?
Vessels made from dead xylem cells. They transport water and nutrients from the soil. They are one way only and have no end walls between cells. They have thick walls stiffened with lignen.
What are phloem?
They are vessels made from living cells. They transport food. The cells have end walls with perforations. They have two way flow.
What is the process of transpiration?
Water is collected by the roots through osmosis
As the plant receives sunlight, water evaporates through the stomata
The water that evaporates creates suction, drawing up more water through the xylem to the leaves.
What are the factors affecting transpiration?
Wind/ air flow
How does light intensity affect the rate of transpiration?
More water needs to be drawn up to allow the increased rate of photosynthesis, so the stomata open more, increasing the rate of transpiration
What is a potometer?
A piece of apparatus that measures water uptake by a plant to measure transpiration rate
How does temperature affect the rate of transpiration?
When it is warm particles have more energy to evaporate and diffuse out of the stomata, so transpiration happens faster
How does air flow affect the rate of transpiration?
With a good airflow water vapour surrounding the leaf is swept away, so there is a low concentration outside the leaf, so diffusion is quicker, so transpiration is quicker
What are auxins?
Plant hormones that control growth at tips of shoots and roots. It is produced in the tips and diffuses backwards to stimulate cell elongation. It promotes growth in the shoot but inhibits growth in the root.
What is positive phototropism?
Growing towards light
What is positive gravitropism?
Growing towards gravity
What is negative phototropism?
Growing away from light
What is negative gravitropism?
Growing away from gravity
Are shoots positively or negatively phototropic? Why?
Positively, as when it is exposed to light it accumulates more auxin on the side in the shade, making it grow faster on the shaded side, so it bends towards light
Are shoots positively or negatively gravitropic? Why?
Negatively, as when it is growing sideways it accumulates more auxin on the lower side from gravity, making it grow faster on the lower side, so it bends upwards
Are roots positively or negatively phototropic? Why?
Negatively, as when it is exposed to light it accumulates more auxin on the side in the shade, inhibiting growth on the shaded side, so it bends downwards, back into the ground
Are roots positively or negatively gravitropic? Why?
Positively, as when it is growing sideways it accumulates more auxin on the lower side from gravity, inhibiting growth on the lower side, so the root bends downward
How can plant hormones be used?
As selective weedkillers, growing from cuttings with rooting powder, controlling flower and fruit formation, producing seedless fruit, controlling ripening of fruits, controlling seed germination.
How can plant hormones be used as selective weedkillers?
They are developed from auxins, which only affect broad leaved plants, which are generally weeds. This disrupts normal growth patterns, killing them, while leaving narrow leaved crops alone
How can plant hormones be used to grow from cuttings with rooting powder?
A cutting is a cut off part of a plant. Normally they will not grow, but if you add rooting powder, containing auxins, it will produce roots and start growing as a new plant. This is used to clone a good plant
How can plant hormones be used to control flower and fruit formation?
Gibberellins stimulate seed germination, stem growth and flowering. They can make plants flower earlier or under different conditions. They can also reduce flower formation, which can improve fruit quality
How can plant hormones be used to produce seedless fruit?
Fruit normally only grows on flowering plants that have been germinated. Gibberellins applied to unpollinated flowers can make fruit grow without seeds
How can plant hormones control the ripening of fruit?
Fruit can be picked when it is unripe as it is firmer and ripened with ethene on the way to the supermarket
How can plant hormones be used to control seed germination?
Lots of seeds will not germinate until they have been through certain conditions. They can be treated with gibberellins to make them germinate at different times of year, and to make all seeds in a batch germinate at the same time
How can you investigate the effect of light intensity on the rate of photosynthesis?
Place Canadian pondweed into a container with water. Add sodium hydrogencarbonate to make sure there is enough CO2. Put a source of white light a specific distance away. Leave it for a set amount of time while counting bubbles/ use a gas syringe. Repeat with the light source at different distances.
How does temperature affect the rate of photosynthesis?
As temperature increases, the rate of photosynthesis increases too as enzymes work better. However, past a point the enzymes become denatures (at ~45 degrees)
What are root hair cells and what do they do?
They are on the surface of plant roots and have a ‘hair’ which sticks out into the soil, giving the plant a large surface area. They absorb water by osmosis and mineral ions by active transport from the soil
What are stomata?
Tiny pores on the surface of a plant, usually on the lower surface of leaves. They allow CO2, water vapour and oxygen to diffuse in and out of a leaf
What are guard cells?
They surround stomata and change shape to control the size of the pore. When they are turgid the stomata are open and when they are flaccid the stomata are closed.
How can you estimate transpiration rate?
Set up a potometer with an air bubble along a capillary tube. As the plant transpires, it takes up water so the bubble moves along. Wait for about an hour and measure how far the bubble has moved.
How are leaves adapted for photosynthesis?
Leaves are broad for a large surface area
The upper epidermis is transparent to allow light through
Palisade cells have lots of chloroplasts and are near the top for more light
The spongy mesophyll contains air spaces to increase diffusion rate
Epidermal tissues are covered with a waxy cuticle to reduce water loss
How are some plants adapted to live in deserts?
Small leaves or spines to reduce surface area for water loss
Curled leaves or hairs to reduce air flow and trap water vapour
Thick waxy cuticles to reduce evaporation
A thick fleshy stem to store water
Fewer stomata that only open at night
Sunken stomata in pits to reduce air flow
How can you investigate plant growth?
Put some cress seeds in a Petri dish lined with moist filter paper. Surround the Petri dish with black card; cut a hole in one side of the card. Shine a light into the box through the hole. Leave the cress seeds for one week and observe the response - they should be growing towards the light.