Topic 7 - Photosynthesis and Food Production Flashcards
Photosynthesis
the process by which plants make their own food by converting light energy from the sun into chemical energy, which is stored in the glucose
Adaptations of leaves for photosynthesis
- broad and flat to increase surface area for sunlight absorption
- chloroplasts are found in the palisade layer, so they’re near the top where they can get the most light
- upper epidermis is transparent so light can pass through to the palisade layer
- vascular bundles transport water and nutrients to every part of the leaf
- waxy cuticle helps reduce water loss by evaporation
Light limiting factor
as light intensity increases, the rate of photosynthesis increases up to a certain point where temperature or CO2 becomes the limiting factor
Carbon dioxide limiting factor
as carbon dioxide concentration increases, the rate of photosynthesis increases up to a certain point where temperature or light becomes the limiting factor
Temperature limiting factor
as temperature increases, the rate of photosynthesis increases up to a point. If the temperature is over 45˚C, enzymes denature and rate of photosynthesis decreases
Testing a leaf for starch
- Heat leaf in boiling water for 10 seconds to denature the enzymes and stop chemical reactions
- Put the lear into a test tube of alcohol. Stand test tube in the beaker of hot water for 10 mins. This will decolourise the leaf
- Rinse leaf in water to remove alcohol and rehydrate it
- Put leaf in white tile cover with iodine solution
- A blue/black colour shows that starch is present
Nitrates
Contain nitrogen for making amino acids and proteins, which are needed for cell growth. If a plant can’t get enough nitrates, leaves will turn yellow
Phosphates
Contain phosphorus for making DNA and cell membranes. They’re needed for respiration and growth. Deficiency causes poor root growth and their older leaves are purple
Potassium
Help enzymes needed for photosynthesis and respiration. Deficiency leads to poor flower/fruit growth and discoloured leaves
Magnesium
Needed to make chlorophyll. Deficiency leads to yellow leaves
Xylem
Carry water and mineral salts from the roots to the leaves
Phloem
Transports sugar and amino acids to different parts of the plant
Adaptations of leaves for gas exchange
- Thin (short diffusion distance for gases)
- Broad (large surface area for diffusion)
- Air spaces allow gases to move easily between cells
- Stomata control diffusion of CO2 and oxygen
- Guard cells control the opening and close of stomata
Fertilisers
substances that provide essential minerals for plant growth to increase crop yield
How to create ideal conditions for photosynthesis
- enclosing plants in glasshouses or polythene tunnels keep them free from pests and disease
- artificial light is supplied after dark to give plants more time to photosynthesise
- increasing the level of carbon dioxide (e.g. by using a paraffin heater)
- increasing temperature by using thermostat heaters and fans
- increasing level of water by using a sprinkler system
- soil pH control - add limestone to increase pH and peat to decrease pH
Pesticide
Chemicals sprayed on crops to kill pests that can also accidentally kill other wildlife (e.g. bees)
Advantages of chemical pesticides
- quick + easy
- increases crop yield
- avoid problems associated with introducing a new predator (e.g. cane toad)
Disadvantages of chemical pesticides
- pollutes water and soil
- kills other harmless organisms (reduction of biodiversity)
- affects the health of humans
- bioaccumulation of toxins as you go up the food chain
- pesticide resistance to create super pests
Advantages of biological control
- Long lasting (don’t need to reapply)
- No bioaccumulation
- Specific to the pest you want to kill
Disadvantages of biological control
- Can’t control where they go
- Not localised
- Can outcompete native species (e.g. for food)
Hydrogen carbonate indicator
Used to show carbon dioxide concentration in a solution
- Purple = low CO2 level = photosynthesis > respiration
- Red = atmospheric level = photosynthesis = respiration
- Yellow = high CO2 level = photosynthesis < respiration
Chlorophyll
A photosynthetic pigment in chloroplasts that absorbs light energy for photosynthesis
Waxy cuticle
The top layer of a leaf that prevents evaporation of water from the surface of the leaf
Limiting factor
a variable that, when in short supply, reduces the maximum rate of photosynthesis
Stoma
a part of the leaf that controls gas exchange
Leaf
an organ of the plant that produces food for the plant through photosynthesis
Biological controls
The introduction of an animal to a crop field to kill pests by predating them
Bioaccumulation
when toxins build up (accumulate) in a food chain
epidermis
A single layer of cells that covers the leaf. It provides a protective barrier against mechanical injury and infection
Iodine
an indicator that turns from orange-brown to blue-black in the presence for starch
chloroplast
the site of photosynthesis in a palisade cell
plant pest
something that can directly or indirectly injure, cause damage to, or cause disease in a plant