Nutrition for N(A)-Level Science (Biology): photosynthesis and its limiting factors, how the leaf is adapted, and human digestion and absorption

What this module covers

Nutrition is about how living things obtain food. Plants make their own food by photosynthesis, and animals take in food and break it down by digestion. You need to know the word equation for photosynthesis and the factors that limit its rate, how the leaf is built to carry out photosynthesis efficiently, and how the human digestive system breaks food down and absorbs it.

This overview links every dot point in the module. Work through them in order, then check yourself with the questions at the end. See the full set at /sg-n-level/biology/syllabus.

Photosynthesis

Start with how plants make food. The page on photosynthesis gives the word equation, the raw materials and conditions needed, what the products are used for, and the limiting factors that affect the rate. Carbon dioxide and water combine, using light energy absorbed by chlorophyll, to make glucose and oxygen.

Leaf structure and adaptations

Next, the organ that does the work. The page on leaf structure and adaptations describes the main parts of a leaf and explains how the broad flat shape, the palisade layer, the stomata and the veins are each adapted for efficient photosynthesis and gas exchange.

The human digestive system

Finally, how animals process food. The page on the human digestive system describes the parts of the gut, the difference between physical and chemical digestion, and how digested food is absorbed in the small intestine, where the villi provide a large surface area.

How this module is examined

At N(A) level there is no standalone pure Biology paper. Biology is taken as part of a combined Science subject, either Science (Physics, Biology) syllabus 5106 or Science (Chemistry, Biology) syllabus 5107, so this module is examined within whichever combination your school offers.

• Learn the equation. Photosynthesis questions reward the full word equation with light and chlorophyll noted as conditions.
• Explain limiting factors. Describe the rise and the plateau on a rate graph and name the factor responsible for each part.
• Pair feature with function. For both the leaf and the small intestine, link a named adaptation to the job it makes possible.

Check your knowledge

A mix of recall, explanation and application questions. Attempt them, then check against the solutions.

1. Write the word equation for photosynthesis. (2 marks)
2. Explain why increasing light intensity stops raising the rate of photosynthesis after a point. (2 marks)
3. State two ways the leaf is adapted for photosynthesis. (2 marks)
4. Explain the difference between physical and chemical digestion. (2 marks)