KS3 Biology › Diet and exercise
KS3 Biology › Diet and exercise
These are the points the worksheet questions are built around.
The human body needs seven separate food groups to work properly, yet one of them is never actually broken down at all. Fibre passes through the digestive system untouched, and that single oddity is a useful way into the wider idea of a balanced diet: getting the right amount of each food group, because each one does its own distinct job.
Most foods are not pure examples of a single group. A slice of toast, for instance, supplies mainly carbohydrate but also carries a little protein, some fibre and a few minerals alongside it. Describing a food as a "protein food" simply means protein happens to be the largest part of what it contains, not that it contains protein alone. A single meal such as a vegetable curry with rice demonstrates the same point: the rice supplies carbohydrate, the vegetables contribute vitamins, minerals and fibre, the cooking oil adds fat, a protein source such as tofu covers that group, and a glass of water on the side completes the set.
Carbohydrates are the body's main source of energy. Starchy foods such as potatoes, pasta, rice and bread are broken down into sugars, which the body's cells then use as fuel, including the muscles doing the work of moving. Sweets also count as carbohydrates, but they consist mostly of added sugar with little nutritional value beyond that, so starchy whole foods are the better source of this kind of energy.
Protein is used for growth and for repairing damaged tissue, whether that is a child getting taller or a small wound healing over. It comes from meat, fish and eggs, but also from plant sources such as beans, lentils and tofu, and even peas contain a surprising amount of protein for their size.
Fat has an unfair reputation as something to avoid altogether, but the body genuinely depends on it. It acts as a stored source of energy, forms an insulating layer that helps keep the body warm, and is the main material the membrane around every single cell is built from. Without any fat in the diet, the body would struggle to build new cells properly. Not all fat behaves the same way, though: unsaturated fat, found in foods such as avocados, oily fish and nuts, is the healthier form, while saturated fat, found in butter, cake and fatty meat, is linked to a higher risk of heart disease when eaten in excess. The aim is not to remove fat entirely but to favour the right kind in a sensible amount.
Vitamins and minerals are only needed in small quantities but still do essential work. The skin produces its own vitamin D whenever sunlight reaches it, and this can also be obtained from oily fish and egg yolks; it supports strong bones and teeth and a healthy immune system. Vitamin C, found in fruit and vegetables, keeps cells healthy and helps wounds heal. Among the minerals, iron, found in red meat and dark green leafy vegetables, is used to build red blood cells that carry oxygen around the body, while calcium, found in dairy products and those same leafy greens, builds strong bones and teeth. Eating a wide range of colours of fruit and vegetables helps ensure a good spread of these vitamins and minerals.
Fibre cannot be digested, yet it still matters: it adds bulk to food and helps keep it moving through the gut, and eating enough of it is linked to a lower risk of bowel cancer and type 2 diabetes. Water makes up around sixty percent of the body and is needed for the chemical reactions taking place inside it constantly. Rather than giving a fixed target, health guidance simply suggests drinking enough that urine stays a pale colour.
All of this is brought together by the Eatwell Guide, a UK government picture showing roughly how much of each food group a balanced diet should contain. It replaced an earlier version, the Eatwell Plate, in 2016. Around a third of the guide is fruit and vegetables and another third is starchy carbohydrates, with smaller sections for protein foods, dairy, and a small amount of oils and spreads. Foods such as crisps, biscuits and chocolate sit outside the main groups altogether, fine occasionally but not as an everyday habit, in line with World Health Organization guidance that less than ten percent of energy should come from sugar and no more than around thirty percent from fat.
What counts as balanced is not identical for everyone. A teenager who is still growing and physically active, such as one playing football regularly, needs more protein, carbohydrate and fat than an adult who sits at a desk all day and has stopped growing. A pregnant woman needs extra protein because her body is building another person. Age, activity level and life stage all change what a balanced diet actually looks like for a given individual.
In short: a balanced diet means eating the right proportions of seven food groups — carbohydrates, protein, fat, vitamins, minerals, fibre and water — each supplying the body with something different, from energy and growth to hydration and a healthy gut. The Eatwell Guide sets out roughly what those proportions should look like, but the precise balance a person needs still depends on their age, activity level and stage of life.
These are the words that appear as key term cards in the video — worth knowing cold before the test.
Revising for a test? Key terms, objectives and quiz questions on one printable page.
The 3 questions from the video, one at a time. See if you caught them.
1. Which of these foods is surprisingly high in protein?
Why: Peas are surprisingly high in protein for their size, making them a great option for non-meat eaters.
2. Which of these is NOT a job that fat does in your body?
Why: Repairing tissue is protein's job — fat stores energy, keeps you warm and builds cell membranes.
3. Should every single meal you eat match the Eatwell Guide?
Why: The Eatwell Guide shows balance across a whole day or week, not each separate meal.
Score: 0 out of 3 —
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Diet and exercise
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