Sr. Inter Botany

1. Succulents are known to keep their stomata closed during the day to check transpiration. How do they meet their photosynthetic CO2 requirements?
A. Succulents show CAM pathway. They show light reaction during day time and dark reaction in the night. Thus they get photosynthetic CO2 requirements from light reaction that occurs during day time.

2. Chl-a is the primary pigment for light reaction. What are accessory pigments? What is their role in photosynthesis?
A. The primary pigment for light reaction is Chl-a. It converts radiant energy to chemical energy The other pigments which include Chl b and carotenoids (carotenes and Xanth ophylls) are accessory pigments. Their functions are..
1) They absorb light and transfer it to Chl-a
2) They enable a wide range of wavelength of incoming light to be utilised for photosynthesis
3) They protect Chl-a from photo oxidation or photo bleaching or Solarisation

3. Does ‘dark reaction’ of photosynthesis require light? Explain
A. Dark reaction do not requires light but it needs the product formed in light reaction. Hence it occurs also during day time.

4. How are photosynthesis and respiration are related to each other?
A. Photosynthesis is the source of food and oxygen which are essential and form the basis of life. The oxygen released in it is taken by living organisms (animals) and release CO2. This CO2 in turn taken by the plants. Priestly was the first to propose that green plants take toxic gases released by animals in respiration and
release pure gas (O2) Photosynthesis is anabolic and respiration is catabolic

5. In what type of plants do you come across ‘Kranz’ anatomy? To which conditions are those plants better adapted? How are these plants letter adapted than the plants, which lack this anatomy?
A. We come across Kranz anatomy in the plants with following characters.
1. Mostly grasses
2. The leaves are isobilateral
3. Mesophyll is undifferentiated
4. Bundle sheath cells are big and arranged circularly in the form of a wreath
5. Leaves show chloroplast dimorphism. These are better adapted to high light intensity, high carbondioxide concentration, high temperature. The plants which lack this anatomy are not adapted to such conditions. These plants have both RuBP case (bundle sheath cells) and PEP case (mesophyll cells) and do not show photo respiration.

1. Name the processes which take place in the grana and stroma regions of chloroplasts?
A. Trapping the light energy and synthesis of ATP and NADPH take place in grana. This set of two reactions are light dependent. So it is called light reaction. The biosynthetic phase where in CO2 and water are converted to Glucose by utilising end products of light reaction occurs in stroma. This set of reactions are together called dark reactions as it do not directly depend up on light.

2. Can chloroplasts be passed on to progeny? How?
A. Yes. chloroplasts can be passed on to progeny. They have genetic material in the form of double stranded circular DNA. They are self reproducing organelles.

3. Where is the enzyme NADP reductase located? What is released if the proton gradient breaks down?
A. NADP reductase enzyme is located in the grana thylakoids on the stroma side. Proton concentration gradient is established along the thylakid membrane between lumen and stroma. The break down of this proton gradient creates energy which is utilised to synthesise ATP.

4. Which tissue transports photosynthates? What experiments prove this?
A. Phloem, the living vascular tissue transports photosynthates in the form of sucrose. Phloem transports food from the leaves upwards and down wards. Thus it is bidirectional. A simple experiment called ‘Girdling experiment’ explains transportation of food.

5. Distinguish between action spectrum and absorption spectrum.
A. A graph showing the rate of photosynthesis at different wave lengths is called Action spectrum. A graph showing the absorption of light by different pigments at different wave lengths is called absorption spectrum.

6. Of the basic raw materials of photosynthesis, what is reduced? What is oxidised?
A. CO2 is reduced. H2O is oxidised.

7. Define the law of limiting factors proposed by Blackman?
A. According to Blackman (1905) “If a process (like photosynthesis) is conditioned as to its rapidity by a number of separate factors the rate of the process is limited by the factor that is present in a relative minimum value”.

8. What is Joseph Priestley’s contribution to the study of photosynthesis?
A. Joseph Priestley discovered that green plants absorb toxic gases released by breathing animals and release O2. He used mint, mouse and candle in the experiment.