Paper 1: Topic 4 Bioenergetics - Photosynthesis (LV) Flashcards
State the word equation for photosynthesis
Carbon dioxide + water → glucose + oxygen
remember to write light and chlorophyll above the arrow between the reactants (left hand side) and products (right hand side)
State the chemical symbol equation for photosynthesis
CO2 + H20 → C6H12O6 + O2
You must be able to write this equation in the correct format for the exam
Describe the process of photosynthesis
Green plants and algae use light energy to convert carbon dioxide and water into glucose and oxygen.
State the raw materials needed for photosynthesis
Explain how the plant obtains both of these raw materials
- Carbon dioxide (obtained from the air when carbon dioxide diffuses into the leaf through the stomata)
- Water (absorbed by the root hair cells and then transported up the plant to the leaves in the xylem by transpiration)
Other than the 2 raw materials what else is needed for photosynthesis to occur
Light
Chlorophyll
Name the waste product of photosynthesis
Oxygen
Define the term endothermic
A chemical reaction that absorbs energy from the environment
In photosynthesis the energy is absorbed from the light and transfered to the chloroplasts
Is photosynthesis an endothermic or exothermic reaction?
Endothermic
State 5 uses of glucose in plants
- For respiration to produce ATP
- Converted to insoluble starch for energy storage
- Converted to cellulose to make new cell walls
- To produce amino acids to produce new proteins for growth and repair of tissues and organs
- To make oils or lipids for energy storage in seeds
What nutrients do plants need to make amino acids?
Glucose (from photosynthesis) and nitrate ions (taken up from the soil by root hair cells)
State 3 reasons why plants store starch
- It is does not affect the water potential of the cell
- It is insoluble
- It stores a lot of energy per molecule
Where do plants store starch?
In their roots, stems and leaves
State 3 factors that affect the rate of photosynthesis
3 from
- Temperature
- Light
- Concentration of carbon dioxide
- Amount of chlorophyll present
State 3 aspects of light that affect the rate of photosynthesis
- Wavelength (not all wavelengths can be used by plants)
- Duration (length of time there is light)
- Intensity (how much light is available)
Define the term ‘limiting factor’
The variable that limits the reaction from occurring any faster
What are the 4 limiting factors that can affect the rate of photosynthesis?
- Temperature
- Light
- Concentration of carbon dioxide
- Quantity of chlorophyll in the leaves
HINT: do NOT say water - this is found in all plants cells and therefore very very rarely a limiting factor
Describe a situation when carbon dioxide may be a limiting factor for photosynthesis
At night when the stomata are closed
This prevent gas exchange occurring in the leaf
Describe a situation when temperature may be a limiting factor for photosynthesis
A cold winter’s day when air temperatures are very low
Describe a situation when light intensity may be a limiting factor for photosynthesis
Night time!
Or a very cloudy day
Describe a situation when chlorophyll may be a limiting factor for photosynthesis
When the plants are deficient in magnesium (referred to as environmental stress)
If the plant has a disease such as tobacco mosaic virus (reduces the amount of chlorophyll)
What is meant by the term environmental stress
When a plant can’t obtain all the nutrients it requires for healthy growth e.g. lack of mineral ions, lack of water (drought)
How can the rate of photosynthesis be studied
Measure the volume of oxygen produced in a given period of time
How can oxygen production be measured?
- By the displacement of water using an upturned measuring cylinder filled with water
OR
- By collecting the gas in a gas syringe
How can you ensure that carbon dioxide is not a limiting factor when investigating the rate of photosynthesis?
Study the rate of photosynthesis using an aquatic plant
Add hydrogen carbonate to the water to ensure an excess of carbon dioxide is available
How can you prevent temperature affecting the rate of photosynthesis if you are investigating the effect of light intensity?
- Use a heat screen between the plant and the light source e.g. a beaker filled with water to absorb the heat energy emitted from the light bulb
Or
- Use a set of apparatus that can be immersed in a thermostatically controlled waterbath
At what temperature do photosynthetic enzymes usually become denatured?
450C
Give an example of a situation where photosynthetic enzymes may get denatured
In a greenhouse on a hot, sunny day
Explain why counting bubbles is not an accurate method of measuring the rate of photosynthesis
- The size and volume of the bubble can vary
- Bubbles evolve at a very fast rate resulting in inaccurate counting
- Some bubbles may remain trapped on the underside of the leaves and not rise to the surface for counting
Explain why white light is best used when investigating the rate of photosynthesis in a laboratory
White light covers a wide range of wavelengths of light (~390-700nm) so should result in faster photosynthesis
Describe how to calculate light intensity
1 divided by the distance squared
Light intensity = 1/d2
Describe how greenhouses help artificially create optimal conditions for farming
- Greenhouses trap light
- They also heat up quickly as the Sun’s heat gets trapped
- The raised temperature and a good source of light both increase photosynthesis
State 2 reasons why it is important to ventilate a greenhouse in the summer
- To prevent the temperature rising about 45oC as this would denature the enzymes involved in photosynthesis
- To maintain air circulation to ensure there is a sufficient carbon dioxide available
Suggest and explain 2 ways a gardener could increase the rate of photosynthesis in his greenhouse during winter
Suggestion 1:
Use a paraffin heater
This will give out heat (increase enzyme activity)
And it will produce carbon dioxide as a water gas (a raw material for photosynthesis)
Suggestion 2:
Use special lighting
This will emit the most efficient wavelengths of light for the plants It will increase light intensity and duration (to overcome the short winter daylight hours)
State 4 factors that a gardener must consider when evaluating the effectiveness of a greenhouse
- Cost of lighting
- Cost of heating
- Cost of fertilisers
- Cost of pesticides & insecticides
Explain why some gardeners use paraffin heaters in their greenhouses
- This will increase the temperature (increase enzyme activity)
- And it will produce carbon dioxide as a waste gas (which can then be used as a raw material for photosynthesis)
Explain why some gardeners use light bulbs that emit specific wavelengths of light rather than white light
This will emit the most efficient wavelengths of light for the plants
It will increase light intensity
Using any light bulbs will increase light intensity and duration (to overcome the short winter daylight hours)
Why do plant cells convert glucose to starch?
Try to think of 2 reasons
- Starch is insoluble and can be used to store glucose
- Starch can be broken down to release glucose which can then be used by the cells for respiration
What test would you carry out to show the presence of lipids?
What would you observe if lipids are present?
Test: Sudan (III)
Positive result: 2 layers form. The top layer will be red.
What test would you carry out to show the presence of sugars?
What would you observe if sugars are present?
What would you observe if no sugars are present?
Test: Benedicts test (Copper sulfate solution) added to a sample of the food and then placed in a water bath at 80oC
Positive result:
Green - Yellow - Orange - Brick red
Negative result: Solution remains blue
What test would you carry out to show the presence of starch?
What would you observe if starch is present?
What would you observe if no starch is present?
Test: Add iodine solution
Positive result: Blue-black colour
Negative result: solution remains yellow-brown
When testing a leaf for the presence of strach why must the plant be placed in an area of bright light before the testis carried out?
To make sure the plant has been exposed to enough light to enable it to photosynthesise
When testing a leaf for the presence of starch why must the leaf first be placed in boiling water?
To remove the waxy cuticle
When testing a leaf for the presence of starch must the leaf be placed in ethanol?
To remove the chlorophyll pigment
If this was not removed the green pigment would mask the colour change of the isiodine solution
Describe how the waste product of photosynthesis is removed from the leaf
The oxygen diffuses from the plant cells into the air spaces inside the leaf
Then the oxygen diffuses out of the leaf to the external atompshere through the stomata
State 3 types of cell that contain chloroplasts
- Palisade mesophyll cells (contains the highest number)
- Guard cells
- Spongey mesophyll cells
Decsribe and explain how temperature affects the rate of photosynthesis
At low temperatures the rate of photosynthesis will be low (as the enzymes are inactive)
As the temperature increases the rate of photosyntheiss increases
The rate of photosynthesis will double for every 10oC rise intemperature upto the optimum temperature of the enzymes used in photosynthesis
After the optimum temperature the rate of photosynthesis will decrease rapidly to zero (as the enzymes are denatured)
Hint: remember when temperature increases remember the rate of diffusion will also increase as the molecules have more kionetic energy
This means the plant cells will be able to take up more carbon dioxide faster as the temperature increases
General maths: exam questions often ask you to calculate various answers. Typical questions can be to
a) calculate a mean
b) calaculate the percentage increase in a variable
Describe how you would calculate these values
Calculating a mean
Add all the values together and then deivide by the number of pieces of data
Calculating the % increase in a variable
Change in the variable x 100
Original variable
