B8 Photosynthesis Flashcards
What is photosynthesis?
Photosynthesis is an endothermic reaction in which energy is transferred from the environment to the chloroplasts by light
Where does photosynthesis take place?
The leaves of the plant are where most photosynthesis takes place, in specialised mesophyll cells which are packed with chloroplasts containing chlorophyll to absorb as much light energy as possible
State the equation for photosynthesis
Carbon dioxide + Water - Light - glucose + oxygen
Is photosynthesis an endothermic or exothermic reaction and why?
Endothermic - energy is transferred from the environment to chloroplasts by light
What are the sugars produced by photosynthesis used for?
The sugars produced by photosynthesis are used to make all the substances a plant needs, as well as being used in respiration to release energy
The glucose produced in photosynthesis may be:
Used for respiration (both aerobic and anaerobic)
Converted into insoluble starch for storage in the stems, leaves and roots
Used to produce fat or oil for storage (especially in seeds)
Used to produce cellulose, which strengthens the cell wall
Combined with nitrate ions absorbed from the soil to produce amino acids for protein synthesis (see picture pg 15-17 savemyexams)
What are the factors affecting photosynthesis?
- The availability of light and carbon dioxide can affect how much and how quickly (the rate) photosynthesis occurs
- Although water is necessary for photosynthesis, it is not considered a limiting factor as the amount needed is relatively small compared to the amount of
water transpired from a plant so there is hardly ever a situation where there is not enough water for photosynthesis - Other environmental factors such as temperature and the amount of chlorophyll in the chloroplasts can also affect the rate of photosynthesis
How does temperature affect photosynthesis?
The temperature of the environment affects how much kinetic energy all particles have – so temperature affects the speed at which carbon dioxide and water move through a plant. The lower the temperature, the less kinetic energy particles have, resulting in
fewer successful collisions occurring over a period of time. Increasing temperature increases the kinetic energy of particles, increasing the
likelihood of collisions between reactants and enzymes which results in the formation of products
At higher temperatures, however, enzymes that control the processes of photosynthesis can be denatured (where the active site changes shape and is no longer complementary to its substrate) – this reduces the overall rate (see chart on Savemyexams)
How does light affect photosynthesis?
The more light a plant receives, the faster the rate of photosynthesis
This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply (see chart on Savemyexams)
IMPORTANT: When light increases the rate of photosynthesis increases as the number of collisions between substrates and enzymes increases. After the optimum temperature is reached, the enzymes begin to denature and rate decreases. So the effect of low temperature is a reduced rate of collisions occurring, and the effect of high temperatures is that enzymes denature.
How does Carbon Dioxide affect photosynthesis?
Carbon dioxide is one of the raw materials required for photosynthesis. CO2 is required to make glucose
This means the more carbon dioxide that is present, the faster the reaction can occur
This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply (see chart on showmyexams)
How does chlorophyll affect photosynthesis?
The number of chloroplasts (as they contain the pigment chlorophyll which absorbs light energy for photosynthesis) will affect the rate of photosynthesis
The more chloroplasts a plant has, the faster the rate of photosynthesis
The amount of chlorophyll can be affected by:
diseases (such as tobacco mosaic virus)
lack of nutrients (such as magnesium)
loss of leaves (fewer leaves means fewer chloroplasts)
How can you show that a plant gives off oxygen during photosynthesis?
Using a water plant (eg pondweed), The most commonly used method to measure the rate of photosynthesis is to measure or observe the oxygen released from aquatic plants
(see picture pg 13 savemyexams)
How is light intensity calculated?
The inverse square law shows the relationship between light intensity and
distance.
As the distance increases the light intensity decreases. This means that they are inversely proportional to each other
This is called the inverse square law and shown by the equation below: Light intensity = 1 / Distance squared
Give examples of leaf adaptation which maximise the rate of photosynthesis
- Broad leaves - maximise the surface area
- Thin leaves - short diffusion distance
- Chlorophyll present - traps light energy
- Veins - transport water to leaves via xylem, remove photosynthesis products via phloem
- Air spaces - allow CO2 to enter and O2 to leave
- Guard cells - control opening of stomata foe gaseous exchange and prevent water loss
Why do Commercial horticulturists will grow their plants in a greenhouse?
Because they are able to control as many of the limiting factors of photosynthesis as possible. Limiting factors are important in the economics of enhancing the conditions in greenhouses to gain the maximum rate of photosynthesis while still maintaining profit
Keeping plants in a greenhouse has associated costs, but the increased yield of the crop and fact that the crop can be harvested more frequently, means
that the farmer will make more money.
The levels of heat, light, water, carbon dioxide and nutrients are carefully controlled so only the smallest amounts needed are used so that farmers are not
wasting money
Eg. spending money on increasing the concentration of carbon dioxide beyond a point when some other factor limits the rate of photosynthesis is a waste
What are the advantages of growing in a greenhouse?
- Artificial light is used for winter/ darker hours
- Heater burns paraffin and produces CO2
- Watering systems to make sure plants are well watered
- Makes it easy to keep away pests and diseases and add fertilizers
- sun heat is trapped in so that temperature does not limit photosynthesis
- ventilation so plants do not get too hot
