Theory question 103
Population Ecology(a) (i) Define the term population (ii) List two biotic and abiotic factors each that affect population growth.
(b) What are the effects of food shortage on a population?
(c) Describe two methods each for: (i) improving crop yield; (ii) preserving and storing food. Explain the principle involved in each of the methods described for preserving and storing food.
Show the model answer
(a)(i) A population is the total number of organisms of the same species living in a given area at a given time
(ii) Biotic (two): food availability, predators, disease/pathogens, competition, parasites; Abiotic (two): water/rainfall, temperature, light, space, soil nutrients
(b) Competition; emigration; starvation, malnutrition and death; reduced birth/reproduction rate; disease; population falls
(c)(i) Any two: use of fertilizers/manure; improved (high-yielding) seeds; irrigation; pest and disease control; crop rotation; mechanised farming
(ii) Any two with principle: drying/smoking – removes water so microbes cannot grow; refrigeration/freezing – low temperature slows microbes and enzymes; salting/sugaring – draws water out of microbes by osmosis; canning – heat kills microbes and sealing keeps others out; chemical preservatives (vinegar, etc.) – stop microbial activity
For each preservation method say why microbes can no longer spoil the food.