National 5 NAR revision Life on Earth

Photosynthesis Photosynthesis is a two-stage process. Stage 1 – Light Reactions Stage 2 – Carbon fixation

Light reactions Light energy is trapped by the chlorophyll in chloroplasts. The light energy is used to split water into hydrogen and oxygen and make ATP. The ATP and hydrogen are used in the second stage but oxygen diffuses out of the cell.

Carbon fixation Carbon fixation is where hydrogen and carbon dioxide are joined together to make glucose. Enzymes are essential in this stage. The glucose can be used for respiration immediately or it can be stored as starch or used to make cellulose for cell walls.

Food Webs The producer is always the first organism in a food chain or web The first organism that eats a producer is the primary consumer If a primary consumer died out, the producer numbers would increase and the number of secondary consumers would decrease

Pyramid of Numbers A pyramid of numbers shows the relative numbers of organisms at each level of a food chain In a pyramid of numbers, the organism at the bottom is always the producer, followed by the primary consumer above it and the secondary consumer at the top

Measuring Abiotic Factors Light intensity can be measured using a light meter To minimise errors when sampling the light in an area, we would take multiple readings at the same time of day and also ensure no shadow is cast on the meter

Temperature is measured using a thermometer To minimise errors when using a thermometer, allow the reading to stabilise and if using a soil thermometer, wipe the probe between readings

pH is measured using a pH meter To minimise errors when sampling pH we would wipe the probe between readings

Adaptation, Natural Selection and Evolution Mutations are a random and spontaneous change in genetic material Mutagenic agents such as radiation, (x-rays, gamma rays, UV rays) and chemicals cause an increase in mutation rate

Natural selection allows the best adapted organisms to survive and pass on their favourable genes to future generations Speciation occurs after a population has become isolated by an isolation barrier. These can be geographical, ecological or behavioural barriers

Human Impact on the Environment When pesticides are sprayed onto crops, this affects other organisms in the food chain. Pesticide toxicity can build up and accumulate in the bodies of organisms higher up the food chain e.g. the organism at the top of the food chain will have the highest toxicity levels from the pesticide As an alternative to pesticides, biological control can be used e.g adding ladybirds to a bush to get rid of greenflies