Bioenergetics Flashcards
What is meant by photosynthesis?
An endothermic reaction by which energy is transferred from the environment to the chloroplasts by light to make nutrients such as glucose.
Where does photosynthesis occur?
In the chloroplasts of a plant.
Explain how plants make glucose
- Photosynthesis occurs in the chloroplasts, which contain a green pigment responsible for the absorption of light to provide energy for photosynthesis to occur. This is called chlorophyll
- Light energy is absorbed by plants chlorophyll.
- Light energy is then uses CO2 from air, and H2O from soil to produce glucose and oxygen.
- This is an endothermic reaction because energy is transferred from surroundings to the reaction.
Equation for photosynthesis:
Carbon dioxide + Water -> Glucose and Oxygen
6CO2 + 6H2O -> C6H12O6 + 6O2.
True or false, photosynthesis is endothermic?
True. Photosynthesis is an endothermic reaction.
State and explain
6 ways leaves are adapted for photosynthesis.
(Love To Chomp Very Amazing Grapes)
Large surface area/Broad - more sunlight can fall onto is so more light energy can be absorbed by chlorophyll, so photosynthesis occurs quicker
Thin - shorter distance for diffusion of gases, eg CO2 and waste O2 - so photosynthesis occurs quicker.
Chlorophyll - Pigment responsible for light energy absorption, for photosynthesis to occur
Veins - Used to transport ALOT of WATER from xylem to cells, so photosynthesis occurs quicker, and used to remove WASTE products of photosynthesis through the phloem.
Air spaces - more CO2 and can enter cells, and more O2 can leave cells, via diffusion so photosynthesis rate increases+ maintains conc gradient to increase diffusion rate
Guard cells - Open and closes stomate to regulate gas exchange to MAKE THE MOST of photosynthesis.
Give a short explanation as to how algae are adapted to photosynthesis in water?
- Large surface area/broad - so can absorbed more CO2 DISSOLVED IN WATER AROUND THEM. and more O2 can dissolved in water around them to be released as a waste product.
State 4 factors affecting the rate of photosynthesis:
- Light intensity
- Carbon dioxide concentration
- Temperature of surroundings.
- Amount of chlorophyll in leaves
How can chlorophyll be reduced in leaves? x3 ways.
1 - Diseases.
2 - Lack of nutrients
3 - Environmental stress (eg pollutants etc)
If the 4 factors affecting the rate of photosynthesis are REDUCED below the optimal requirement, what will happen to the rate of photosynthesis?
It will decrease.
How can CO2 conc be increased for photosynthesis? X3
- Respiration
- Combustion of fossil fuels
- Putting plant in a dark place.
A student places a plant in a dark environment and notices that carbon dioxide conc in surroundings increases after measuring it - suggest why.
- Bc dark, less light absorbed.
- Less photosynthesis (so CO2 is used less)
- But still respiration still occurs (so CO2 in surroundings increases)
- So CO2 made is more than being used
- So conc of CO2 in surroundings increases.
Explain how temperature affects photosynthesis? - you must refer to enzymes in your answer.
- Temperature increase means more thermal energy provided so no. of collisions between reacting particles (CO2 AND H2O) increases so rate of photosynthesis increases.
- Temp increase also means enzyme activity increases, so does rate of reaction.
- If temp increase too high, past optimal level (45 deg celc), enzymes will begin to denature, so rate of photosynthesis decreases.
At night a limiting factor for photosynthesis would be?
Light intensity.
In the winter, what would be a limiting factor for photosynthesis?
Temperature of surroundings
In light and warm conditions what would be a limiting factor for photosynthesis?
Carbon dioxide concentration.
In mineral-deficient soil what would be a limiting factor for photosynthesis?
Chlorophyll (less minerals absorbed by plants, so less chlorophyll made)
What is meant by a limiting factor?
A factor that if in low levels, it restricts the increase in rate of reaction as well as the reaction from occurring at the maximum rate.
On a graph, which axis will the ‘factor’ and ‘rate of photosynthesis’ go on.
X-axis - factor (CO2 conc, light intensity etc)
Y-axis - rate of photosynthesis
How are greenhouses used to make the most of photosynthesis? (Think of photosynthesis factors and apply)
- To increase light intensity - artificial light sources eg LED as well as natural light.
- Temperature - from heat sources eg electric heater and paraffin heats
- extra CO2 - paraffin heaters (fossil fuel burnt - CO2 produced)
- Ventilation - Temperature is regulated - for optimal enzyme activity
- Watering system
- Greenhouse glass - traps heat, light can enter
- Plants kept inside green houses - away from pests, can be monitored and controlled w pesticides and fertilisers
IN AN EXAM: state, explain how this makes the most of photosynthesis + state how that prevents a particular factor from being a limiting factor.
What is a disadvantage of using a greenhouse? x 1
- Expensive, because a lot of energy (thermal and light) is required.
- So extra cost must be justified by the yield of plants produced.
what are the advantages of greenhouses? x 2
- Increase in crop yield, so more profitable.
- Plants can be closely monitored away from pests.
How do plants use glucose?
- Respiration glucose + oxygen -> CO2 + H2O
- To make cellulose (for cell structure - to strengthen cell wall)
- To make starch (to be converted intro insoluble starch for storage, so when conditions aren’t favourable for PS, they still have food)
- To make amino acids to make proteins - (glucose combines w nitrate ions which are absorbed from soil to make ACs)
- To make oils and fats (store of energy in plant seeds, this is useful bc when planted, the new plant will hv energy to respire as it germinates, leading to healthy growth)
Why is starch sometimes more ideal than glucose?
- Starch is insoluble so will not absorb water from soil via osmosis, while glucose would.
- So starch is a more reliable and better energy source for plants.
- Especially when photosynthesis isn’t occurring due to unfavourable conditions.
Why are algal cells considered a source of biofuels?
Because they are rich in fats and oils, so can be burnt to produce energy.
How can we test for the presence of starch in plants?
1 - Drop leaf into BOILING water. (to kill the cells and break down membranes - to extract chlorophyll and allow iodine to enter into cells to react w starch)
-2 Remove leaf and place into hot ethanol for 10-15 minutes (longer time means colour change is seen more clearly).
- Leaf becomes whiter when ethanol is added (bc ethanol dissolves the chlorophyll
-3 Now place leaf on a white tile and add 1-2 drops of iodine.
- If starch is present leaf becomes orange-red (if kept in the dark) or blue-black (if kept in light)
Describe a practical to investigate the effect of light intensity on the rate of photosynthesis.
- AIM - to investigate the effect of light intensity on the rate of photosynthesis.
1) Place a piece of pondweed with a cut into a beaker of water, 10cm away from an LED light source (measure distance using a ruler).
2) Add sodium hydrogen carbonate to the water - this produces CO2 gas for plant to photosynthesise to produce O2 gas
3) Once the sodium hydrogen carbonate is added, leave plant to acclimatise to its new conditions for 5 minutes.
4) Now, count the number of O2 gas bubbles produced in one minute - repeat this step 2 more times and calculate a mean.
5) Repeat the previous steps using different distances away from the LED light source.
6) Record date on a table and plot on a graph - we should notice that as distance increases, light intensity decreases, less O2 gas produced so rate of PS falls.
What is meant by the inverse square law?
The law that states light intensity and distance are inversely proportional.