IGCSE Biology / Food and digestion
What changes how much energy you need
Edexcel International GCSE Biology (4BI1), chapter 4: Food and digestion, specification point 2.26. Free lesson.
Read the revision notes · IGCSE Biology past papers
Energy requirements vary with age, sex, activity, pregnancy and breastfeeding. Explaining the reasons, especially how they affect respiration, helps you answer questions about energy needs.
How energy needs change with age
A graph of energy needed per day against age shows the main pattern. Energy needs rise during childhood, reach a peak in the late teens, then fall through adult life. Growth requires energy because the body is building new tissue. Later, muscle mass and activity often decrease, lowering the metabolic rate, which is the rate at which the body uses energy. Teenagers can need more energy than adults because they are growing quickly and are often more active. The male and female lines have a similar pattern, but they are not identical after eighteen. Energy needs can rise during pregnancy and…
How age and sex affect energy needs
Children and teenagers need more energy per kilogram of body mass because they are growing and building new tissue. Older adults may need less as muscle mass and activity decrease. Males typically need more than females because they usually have a greater proportion of muscle, which has a higher metabolic rate than fat. More muscle means more energy is used through respiration, even when comparing people of similar size. The usual differences are patterns, not exact rules for every individual.
How activity affects energy needs
When you do physical activity, your muscles contract. Contracting muscle respires more, so it needs more energy. This is why someone doing manual work or sport may need more energy than someone who is less active. Link activity to muscle respiration when explaining the difference in energy requirements. More energy is released by respiration to meet the muscles' needs.
Why pregnancy and breastfeeding raise energy needs
During pregnancy, extra energy is needed as the fetus grows and the mother's body changes. During breastfeeding, producing milk also requires energy, so the requirement rises further. Pregnancy raises energy needs because new tissue is growing. Breastfeeding raises energy needs because making milk costs energy.
How to explain a difference in energy needs
Use the person's age and activity to give reasons, then link at least one reason to respiration. For example, a teenager may need more than an adult because the teenager is still growing and may be more active.
More lessons in Food and digestion
- Carbohydrates, proteins and lipids
- Testing for starch, sugars, protein and fat
- The seven parts of a balanced diet
- The parts of the digestive system
- Teeth, chewing and peristalsis
- Amylase, protease and lipase
- Bile, the liver and emulsifying fat
- The villus and absorption
- Practical: measuring the energy in a food sample