photosynthesis (topic 4) Flashcards
give one other way of reducing the negative effects of human activity on our ecosystems other than protecting rare habitats
- breeding programmes (for endangered species)
- regeneration (programmes)
- recycling
light
give three ways in which plants use the glucose made in photosynthesis
- for respiration
- to make cellulose / starch
- to make lipid
- to make protein
- chlorophyll is needed for photosynthesis
- light is needed for photosynthesis
- at a light intensity of 250 arbitrary units, light is not a limiting factor of photosynthesis, what is the evidence for this in figure 3
- higher light intensity does not increase rate of photosynthesis
- the graph stays level (above this value)
- stops increasing
- rate of photosynthesis stays the same (above this value)
write the balanced symbol equation for photosynthesis
6 CO2 + 6 H2O ➔ C6H12O6 + 6 O2
explain why photosynthesis is considered an endothermic reaction (1)
it absorbs light energy from the environment
give two uses of the glucose produced in photosynthesis (2)
- respiration (provide energy)
- converted into starch (provide energy when needed)
- converted into cellulose (strengthen the cell wall)
- converted into other molecules/fats/amino acids
describe the relationship between light intensity and the rate of photosynthesis (3)
- the rate of photosynthesis increases with light intensity
- above a certain light intensity/500 lux, the rate of photosynthesis increases at a much slower rate
- suggesting a limiting factor other than light intensity
at light intensities between 0 and 700 lux, light was a limiting factor for photosynthesis, what evidence is there for this in the table (1)
- rate of bubbles increases
- more gas released
what could the students do to make sure that heat from the lamp did not affect the rate of photosynthesis (1)
- add a water bath
- heat screen
- use LED
- low energy bulb
(4)
chloroplasts (max 2 marks):
- chloroplasts
- found mainly in the palisade layer
- where photosynthesis occurs
- contain chlorophyll, which absorbs light energy for photosynthesis
stomata/guard cells (max 2 marks):
- stomata/guard cells
- found on the lower epidermis
- responsible for gas exchange
waxy cuticle (max 2 marks):
- waxy cuticle
- transparent
- helps the plant retain water
in a certain plant species, it is observed that the leaves have fewer stomata than a typical plant, suggest how this could impact the rate of photosynthesis (2)
- fewer stomata could limit the rate of gas exchange
- less carbon dioxide available for photosynthesis
- less reactant reduces the rate of photosynthesis
the plant also has a very thick waxy cuticle, suggest the environment in which the plant lives and why having fewer stomata and a thick waxy cuticle is a useful adaptation (2)
- lives in dry conditions
- plants release water vapour into the air through stomata
- fewer stomata and thick waxy cuticles conserve water
explain the role of carbon dioxide in photosynthesis and how increasing its concentration might affect the rate of photosynthesis (3)
- carbon dioxide is one of the reactants required for photosynthesis
- increasing the concentration of carbon dioxide increases the rate of photosynthesis up to a point
- after this point other factors such as light intensity or temperature may become limiting
to increase the rate of growth of the strawberry plants
- because it would cost more money than using 0.08%
- because it would not increase the rate of photosynthesis any further
during the growing season for strawberries in the UK, natural daylight has an intensity higher than 30,000 lux, the farmer read about the scientists’ work and analysed their graph, the farmer decided to use the following conditions in his greenhouse during the day:
- 20°C
- 0.08% CO2
- no extra lighting
suggest why the farmer may have decided to use these conditions for growing the tomatoes, give reasons for your suggestions (4)
- to make more profit
- raising temperature to 25°C makes very little difference at 0.04% CO2
- at 20°C with CO2 at 0.08%, it raises the rate OR rate doubles
- although 25°C gives a higher rate, the cost of heating not economical
- extra light does not increase rate
- epidermis covers the plant
- epidermis contains no chloroplasts and allows light to penetrate into the leaf
- palisade mesophyll contains many chloroplasts to trap light
- palisade mesophyll is where photosynthesis happens
- spongy mesophyll has air spaces for rapid movement of gases
- phloem transports sugars
- xylem transports water (and minerals)
- waxy cuticle reduces water loss
- stomata (or guard cells) allow CO2 in and O2 out
- stomata (or guard cells) control water loss
the rate of photosynthesis in a plant depends on several external factors, these factors include light intensity and the availability of water, describe and explain the effects of two other factors that affect the rate of photosynthesis, you should include one or more sketches of graphs in your answer (6)
carbon dioxide - effect:
- as CO2 increases so does the rate and then it levels off
carbon dioxide - explanation:
- graph increases because CO2 is a reactant used in photosynthesis
- graph levels off when another factor limits the rate
temperature - effect:
- as temperature increases, so does the rate and then it decreases
temperature - explanation:
- rise in temperature increases the rate of chemical reactions
- because more kinetic energy allows the molecules to move faster
- if the temperature is too high, the rate decreases because the enzymes are denatured
