Exercises: Nutrients, diet and inheritance

Name the six components of a balanced diet. For three of them, give one example of a food that is a good source.

Name the food test used to detect each of the following and state the positive result:

1. a) starch

1. b) reducing sugar (glucose)

1. c) protein

Define the terms "gene", "allele" and "inherited". Give one human characteristic that is inherited.

A packet of oat biscuits states that $100\ \text{g}$ contains $62\ \text{g}$ carbohydrate, $20\ \text{g}$ fat and $7\ \text{g}$ protein. Energy values are $17\ \text{kJ/g}$ for carbohydrate and protein and $37\ \text{kJ/g}$ for fat.

1. a) Calculate the energy from each nutrient in $100\ \text{g}$.

1. b) Calculate the total energy in $100\ \text{g}$.

1. c) A student eats a $35\ \text{g}$ portion. Calculate the energy in this portion.

Lactose intolerance is more common in some populations than in others and depends partly on inherited genes. A person with lactose intolerance lacks enough of the enzyme lactase.

1. a) Explain why the lack of lactase causes problems when the person drinks milk.

1. b) Explain why the condition can run in families.

1. c) Suggest how a person with lactose intolerance can still obtain calcium in the diet.

Cystic fibrosis is an inherited condition caused by a recessive allele. Two parents who are both carriers ($\text{Ff}$) have a child.

1. a) Draw a Punnett square in words or table form for this cross.

1. b) State the probability that the child has cystic fibrosis.

1. c) State the probability that the child is a carrier.

Type 2 diabetes is influenced by both inherited factors and lifestyle. A study in Ireland finds that people with a parent with type 2 diabetes are about $3$ times more likely to develop it, but that within this group, those with a high-sugar, low-activity lifestyle are far more likely to develop it than those with a balanced lifestyle.

1. a) Explain what this shows about the relative roles of genes and environment.

1. b) Suggest three lifestyle changes that could lower the risk.

1. c) Explain why a correlation between diet and disease does not on its own prove causation, and describe how scientists could strengthen the evidence.

Phenylketonuria (PKU) is a recessive inherited condition in which the body cannot break down the amino acid phenylalanine. It is screened for in newborns in Ireland through the heel-prick test. If untreated, phenylalanine builds up and harms the brain. Treated babies follow a low-protein diet.

1. a) Explain why newborn screening is valuable.

1. b) Explain why the condition is controlled by diet rather than cured.

1. c) A couple, both carriers, have two children. Calculate the probability that both children have PKU.

1. d) Discuss one ethical issue related to genetic screening.

A teenage athlete needs about $12,000\ \text{kJ}$ per day and her diet provides $10,200\ \text{kJ}$ per day. She also reports tiredness and is found to have low iron levels.

1. a) Calculate the daily energy deficit and express it as a percentage of her requirement.

1. b) Predict the effect on body mass over several weeks if this deficit continues.

1. c) Explain why iron is needed in the diet and suggest two good food sources.

1. d) Explain why a balanced diet matters, not only the total energy intake.