Biosphere Contents

3. Photosynthesis

Conclusion

The fundamental processes of photosynthesis and respiration have been considered in detail. Through photosynthesis, plants convert carbon dioxide and water, using the sun's energy, to produce organic matter and oxygen. Through respiration, plants and animals break down organic matter and oxygen to produce carbon dioxide and water, releasing energy. These processes occur both for land-based and for aquatic organisms.

Question and answers

1. The two most important processes by which organisms modify the environment are photosynthesis and respiration. Write down the photosynthesis equation.

question 1 answers

2. Write down the respiration equation.

question 2 answers

3. How are the elements necessary for plant growth on land obtained?

question 3 answers

4. What are stomata, and how do they help in the supply of ions to the plant?

question 4 answers

5. Give one example of the way freshwater availability can control total biomass.

question 5 answers

6. What is the limiting nutrient for most natural freshwater ecosystems?

question 6 answers

7. What proportion of the surface incident light must be received by most marine photosynthetic organisms for growth to occur?

question 7 answers

8. Give one reason why soils at low latitudes have a high input of nutrients.

question 8 answers

9. In the aquatic system, what is released into the water column during the decomposition of organic material?

question 9 answers

Question 1 answer

The photosynthesis equation: 6CO2 + 6H2O + energy = C6H12O6 + O2

Question 2 answer

The respiration equation: C6H12O6 + O2 = 6CO2 + 6H2O + energy

Question 3 answer

Generally water, nutrients and trace elements are received from the soil via a root system (the latter two in dissolved forms). Carbon dioxide, however, is extracted from the air.

Question 4 answer

Stomata are pores in the leaves of land plants which allow for the exchange of gases, carbon dioxide being taken up and oxygen and water vapour being lost. The transpiration of water from the leaves through stomata creates surface tension which helps pull a stream of water up the stem from the roots, using transport vessels called xylem. In combination with this, water moves from the soil into the roots due to an osmotic gradient. This stream of water transports dissolved ions from the roots to the leaves.

Question 5 answer

With the mean annual temperature being roughly similar, the vast differences in the amounts of plant matter produced in the tropical rainforests of the Congo Basin, the savannah grasslands of east Africa and the Sahara desert, are due to differences in the availability of water.

Question 6 answer

Phosphorous.

Question 7 answer

Usually more than 1% of the surface light incident must be received.

Question 8 answer

- leaves are the most important single source of organic matter for decomposition; and leaf deposition is proportional to productivity i.e. litterfall decreases with increasing latitude. The litterfall is decomposed by microfauna in the soil layer into the constituent nutrients, which provide the substrate for new plant growth.

- decomposition of high leaf quantities produces simple organic aids, such as acetic acid (CH3 COOH), oxalic acid (COOH)2 and carbonic acid (H2 CO3 ). These acids are important chemical weathering agents for soils and minerals in the soil. Therefore increased organic matter breakdown enhances weathering rates, which can increase the supply of nutrients as long as there remains sufficient material to be weathered.

Question 9 answer

- dissolved nutrients (ammonia, nitrate and phosphate);
- dissolved organic matter; and
- particulate organic matter