The phosphorus cycle

Question 1

Why is phosphorus important ?

Answer 1

Plants and animals require phosphorus in order to produce certain biological molecules such as phospholipids (for cell membranes), nucleic acids (DNA and RNA) and ATP

Question 2

What could be the effects if there was a lack of phosphate ?

Answer 2

less DNA for cell division
less glucose produced in photosynthesis
less respiration therefore less growth
less for membranes and therefore cell division for growth and repair.

Question 3

Explain the phosphorus cycle

Answer 3

Phosphorus in rocks is slowly released into the soil and into water sources in the form of phosphate ions (PO₄³⁻) by the process of weathering (the slow breaking down and erosion of rocks over time)

Phosphate ions are taken up from the soil by plants through their roots or absorbed from water by algae

Phosphate ions are transferred to consumers during feeding
Phosphate ions in waste products and dead organisms are released into the soil or water during decomposition by saprobionts

The phosphate ions can now be taken up and used once again by producers or may be trapped in sediments that, over very long geological time periods may turn into phosphorus-containing rock once again

Question 4

What does Mycorrhizae refer to ?

Answer 4

The relationship between plant roots and fungi

Question 5

Explain why phosphates are essential for plant growth

Answer 5

the production of NADP
The synthesis of ATP
the production of DNA

Question 6

Explain Mycorrhizae

Answer 6

Many plants have evolved symbiotic (mutually beneficial) relationships with fungi

The fungi are composed of long, thin filaments known as hyphae, which interact with the roots of the plants
These hyphae greatly increase the surface area of the root systems of the plants, increasing the amount of water and mineral ions (e.g. nitrates and phosphates) that can be absorbed by the plants’ roots
In return, the fungi receive organic compounds (e.g. glucose) and oxygen from the plant

Question 7

Explain how herbivores obtain phosphorus from their food

Answer 7

absorbing phosphate ions directly from their food
digesting food into smaller phosphate containing molecules such as nucleotides

Question 8

Explain how phosphorus in animals is recycled back into an ecosystem

Answer 8

Animals produce faeces OR animals die;
The phosphorus-containing substances in their faeces or tissues are digested by saprobiotic bacteria
This releases phosphate ions
Phosphate ions can then be taken up again by plants