Diet — Combined Science 0653 - Biology Revision Notes & Topical Questions

Section 1 of 26Balanced diet

Balanced diet

Balanced diet

Balanced diet a diet containing all of the food groups in the correct proportions.

Food groups

• Food groups carbohydrates, proteins, lipids, vitamins, minerals, dietary fibre and water.

Section 2 of 26Functions and sources of the food groups

Food group	Function	Sources
Carbohydrate	Source of energy	Bread, cereals, pasta, rice, potatoes
Protein	Growth and repair	Meat, fish, eggs, pulses, nuts
Lipid (fats and oils)	Insulation and energy storage	Butter, oils, nuts
Dietary fibre	Provides bulk (roughage) so that the intestine can push food through	Vegetables, whole grains
Vitamins	Needed in small quantities to maintain health	Fruits and vegetables
Minerals	Needed in small quantities to maintain health	Fruits and vegetables, meat, dairy products
Water	Needed for chemical reactions to take place in cells	Water, juice, milk, fruits and vegetables

Section 3 of 26Carbohydrates and lipids

Carbohydrates

• Carbohydrates the main source of energy.

Lipids

• Lipids an energy store and insulation.
• Excess energy intake leads to weight gain.

Section 4 of 26Proteins

Growth and repair

• Growth and repair proteins are needed to make new cells and repair damaged tissue.

Lack of protein

• Lack of protein causes poor growth, as in kwashiorkor.

Section 5 of 26Fibre and water

Fibre

• Fibre adds bulk so that food moves through the gut.
• Lack of fibre can cause constipation.

Water

• Water is a solvent and is needed for reactions in cells, but it does not provide energy.

Section 6 of 26Deficiency effects

Nutrient	Deficiency effect
Vitamin C	Scurvy
Vitamin D	Rickets
Calcium	Weak bones and teeth
Iron	Anaemia
Protein	Poor growth
Fibre	Constipation

Section 7 of 26Planning a balanced meal

1

Include a source of carbohydrate for energy.

2

Include a source of protein for growth and repair.

3

Include fruit and vegetables for vitamins, minerals and fibre.

4

Keep fats, sugars and salt in small amounts.

5

Drink enough water.

Section 8 of 26More from the specification

1

Dietary amino acids assimilation

• Dietary amino acids assimilation digestive breakdown of dietary proteins yields essential amino acids absorbed across digestive system organs into bloodstream.

2

Internal organs nutritional requirements

• Internal organs nutritional requirements metabolically active vital organs demand balanced fatty acids and vitamins for normal physiological system functions.

3

Balanced Diet Components and Functions

• A healthy human diet requires balanced proportions of carbohydrates, proteins, lipids, vitamins, mineral ions (calcium and iron), dietary fibre (roughage),
  • and water to sustain cellular metabolism.
  • (such as C and D)

4

Mineral Requirements for Fetal Development

• Pregnant women require supplementary dietary iron to synthesize maternal and fetal haemoglobin, alongside elevated calcium to mineralize embryonic skeletal bones and tooth buds.

5

Prevention of Nutritional Deficiency Diseases

• Inadequate dietary vitamin C causes scurvy with bleeding gums and poor wound healing,
• while vitamin D or calcium deficiency precipitates rickets with soft, malformed bones.

6

Adaptation

• A feature that makes something well suited to what it does.

7

Physical digestion

• Breakdown of food into smaller pieces without chemical change.

8

Amino acid

• The unit from which proteins are made.

9

Enzyme

• A protein that acts as a biological catalyst.

10

Molecule

• Two or more atoms joined together chemically.

11

Duodenum

• The first part of the small intestine.

12

Absorption

• Movement of digested molecules into the blood.

13

Starch

• The storage carbohydrate in plants, which turns iodine blue-black.

14

Emulsification

• Breaking large drops of fat into smaller ones.

15

Organ

• Different tissues working together to carry out a function.

16

Pancreas

• Gland making insulin and glucagon

Section 9 of 26Vitamins and minerals needed

Nutrient	Function	Sources
Vitamin C	Forms an essential part of collagen, found in skin, hair, gums and bones	Citrus fruit, strawberries, green vegetables
Vitamin D	Helps the body to absorb calcium, so it is needed for strong bones and teeth	Oily fish, eggs, liver, dairy products, and made in the skin in sunlight
Calcium	Needed for strong bones and teeth and for blood clotting	Milk, cheese, eggs
Iron	Needed to make haemoglobin, which binds and carries oxygen in red blood cells	Red meat, liver, leafy green vegetables such as spinach

Section 10 of 26Vitamin C

Collagen

• Collagen vitamin C is needed to make this protein, which is found in skin, hair, gums and bones.

Deficiency

• Deficiency a severe lack causes scurvy.

Section 11 of 26Vitamin D

Calcium absorption

• Calcium absorption vitamin D helps the body absorb calcium from the gut.

Made in the body

• Made in the body the skin makes a form of vitamin D when a substance in it is exposed to UV light in sunlight.

Section 12 of 26Calcium

Bones and teeth

• Bones and teeth calcium is a key component of both.

Blood clotting

• Blood clotting calcium is involved in clotting.

Deficiency

• Deficiency a lack can lead to osteoporosis later in life.

Section 13 of 26Iron

Haemoglobin

• Haemoglobin iron is part of the pigment in red blood cells.

Deficiency

• Deficiency too little iron causes anaemia.

Section 14 of 26Varying dietary needs

Factor	Dietary need
Age	Energy need rises towards adulthood for growth, and children need a higher proportion of protein; adults' energy needs fall as they age
Activity level	The more active the person, the more energy needed, because muscles respire more
Pregnancy	More energy for the growth of the foetus and the extra mass carried, plus extra calcium and iron for the foetus's bones, teeth and blood
Breastfeeding	More energy and extra calcium to make good-quality milk

Section 15 of 26Why needs differ

Growth

• Growth children and teenagers need more protein and calcium.

Energy

• Energy an active person or a manual worker needs more energy than an inactive person.

Section 16 of 26More from the specification

More from the specification

Dietary amino acids in vital organs

• Dietary amino acids in vital organs absorbing balanced fatty acids and essential amino acids supports cellular repair across mammalian internal organs.

Human digestive enzymes and substrates

• Salivary and pancreatic amylase digest starch to maltose;
  • gastric pepsin and pancreatic trypsin hydrolyse proteins to amino acids;
  • pancreatic lipase hydrolyses lipids.

Chemical digestion in the stomach and duodenum

• Gastric hydrochloric acid provides optimal pH 1.5-2.0 for pepsin activity and destroys pathogens,
• while alkaline bile neutralises acid in the duodenum.

Villi structure and nutrient absorption

• Intestinal villi and microvilli provide a massive surface area, rich capillary blood supply,
• and lacteals for rapid absorption of monosaccharides, amino acids,
• and fatty acids.

Chemical digestion

• Chemical digestion digestive enzymes chemically hydrolyse large insoluble nutrient molecules into small soluble molecules.

Duodenum digestion

• Duodenum digestion food entering the duodenum from the stomach mixes with pancreatic juices to continue starch digestion.

Small intestine absorption

• Small intestine absorption digested food molecules pass through the epithelial lining of the small intestine into the circulatory system.

Adaptation

• A feature that makes something well suited to what it does.

Chemical digestion

• Breakdown of large insoluble molecules into small soluble molecules.

Physical digestion

• Breakdown of food into smaller pieces without chemical change.

Amino acid

• The unit from which proteins are made.

Dietary fibre

• Plant material that gives bulk to the food in the gut.

Enzyme

• A protein that acts as a biological catalyst.

Molecule

• Two or more atoms joined together chemically.

Duodenum

• The first part of the small intestine.

Starch

• The storage carbohydrate in plants, which turns iodine blue-black.

Emulsification

• Breaking large drops of fat into smaller ones.

Organ

• Different tissues working together to carry out a function.

Pancreas

• Gland making insulin and glucagon

Section 17 of 26Scurvy

1Cause

• Cause a severe lack of vitamin C in the diet for over 3 months.

2Symptoms

• Symptoms anaemia, exhaustion, spontaneous bleeding, pain in the limbs, swelling, gum ulcers and tooth loss.

3History

• History it was common in sailors between the 15th and 18th centuries, because long voyages meant no fresh produce rich in vitamin C.

4Treatment

• Treatment oral or intravenous vitamin C supplements.

Section 18 of 26Rickets

Definition

• Definition a condition in children with poor bone development.

Symptoms

• Symptoms bone pain, lack of bone growth, and soft, weak bones that can cause deformities.

Cause

• Cause a severe lack of vitamin D, which is needed for calcium to be absorbed.

Treatment

• Treatment eat more foods with calcium and vitamin D, or take vitamin D supplements.

Section 19 of 26Preventing rickets

Sunlight

• Sunlight the skin makes vitamin D when a substance derived from cholesterol is exposed to UV radiation.

Foods

• Foods vitamin D is found in fish, eggs and butter.

Section 20 of 26Other deficiency diseases

Disease	Missing nutrient	Effect
Anaemia	Iron	Too little haemoglobin, causing tiredness and pale skin
Kwashiorkor	Protein	Swollen abdomen and poor growth
Constipation	Fibre	Difficulty passing faeces

Section 21 of 26Malnutrition

Undernutrition

• Undernutrition too little food or a lack of protein or energy causes starvation or kwashiorkor.

Overnutrition

• Overnutrition too much energy-dense food causes obesity.
• Obesity raises the risk of type 2 diabetes and heart disease.

Saturated fat

• Saturated fat too much can cause heart disease.

Section 22 of 26Food tests

Nutrient	Test	Positive result
Starch	Iodine solution	Orange-brown to blue-black
Reducing sugar	Benedict's solution, heated	Blue to orange or brick red
Protein	Biuret solution	Blue to purple
Lipid	Ethanol then water	Cloudy emulsion
Vitamin C	DCPIP	Blue dye is decolourised

• Vitamin C amount
  • the smaller the volume of juice needed to decolourise DCPIP, the more vitamin C the food contains.

Section 23 of 26Energy content of food

Burn a weighed sample of food under a boiling tube containing a known mass of water.

Measure the rise in temperature of the water.

Calculate energy in J

Calculate energy in J mass of water in g × 4.2 × temperature rise in °C.

Divide by the mass of food burnt to find J per gram.

• Underestimate
  • the result is too low because heat is lost to the air.

Section 24 of 26More from the specification

More from the specification

Cellular assimilation of amino acids

• Cellular assimilation of amino acids specialised epithelial cells absorb dietary amino acids, distributing them toward metabolic organs for protein synthesis.

Essential fatty acids in bodily organs

• Essential fatty acids in bodily organs human somatic cells require linoleic and alpha-linolenic fatty acids to preserve membrane structural integrity across organs.

Mechanical vs Chemical Digestion

• Mechanical breakdown by teeth and muscular contractions reduces particle size without altering chemical bonds, facilitating subsequent chemical digestion by enzymes.

Chemical Digestion and Digestive Enzymes

• Insoluble dietary macromolecules are broken down into small, absorbable nutrient molecules by hydrolytic enzymes within the digestive system.

Gastric Digestion in the Stomach

• The stomach wall secretes hydrochloric acid and pepsin enzymes to begin the chemical digestion of proteins.
  • (killing pathogens and providing optimum pH 2)

Digestion in the Duodenum and Small Intestine

• In the duodenum, bile emulsifies fats while pancreatic and intestinal enzymes complete the breakdown of carbohydrates, proteins, and lipids.

Mechanical vs Chemical Digestion

• Mechanical breakdown by teeth and muscular contractions reduces particle size without altering chemical bonds, facilitating subsequent chemical digestion by enzymes.

Chemical Digestion and Digestive Enzymes

• Insoluble dietary macromolecules are broken down into small, absorbable nutrient molecules by hydrolytic enzymes within the digestive system.

Gastric Digestion in the Stomach

• The stomach wall secretes hydrochloric acid and pepsin enzymes to begin the chemical digestion of proteins.
  • (killing pathogens and providing optimum pH 2)

Digestion in the Duodenum and Small Intestine

• In the duodenum, bile emulsifies fats while pancreatic and intestinal enzymes complete the breakdown of carbohydrates, proteins, and lipids.

Pancreas

• Gland making insulin and glucagon

Adaptation

• A feature that makes something well suited to what it does.

Physical digestion

• Breakdown of food into smaller pieces without chemical change.

Amino acid

• The unit from which proteins are made.

Dietary fibre

• Plant material that gives bulk to the food in the gut.

Enzyme

• A protein that acts as a biological catalyst.

Molecule

• Two or more atoms joined together chemically.

Duodenum

• The first part of the small intestine.

Absorption

• Movement of digested molecules into the blood.

Emulsification

• Breaking large drops of fat into smaller ones.

Organ

• Different tissues working together to carry out a function.

Section 25 of 26Key terms

Term	Meaning
Balanced diet	A diet with all food groups in the correct proportions.
Carbohydrate	The main source of energy.
Protein	A nutrient needed for growth and repair.
Lipid	A fat or oil used for insulation and energy storage.
Dietary fibre	Plant material that gives bulk to the food in the gut.
Vitamin	A nutrient needed in small amounts to keep healthy.
Mineral	An inorganic nutrient needed in small amounts.
Deficiency disease	An illness caused by a lack of a nutrient.

Term	Meaning
Vitamin C	A vitamin needed to make collagen.
Vitamin D	A vitamin that helps the body absorb calcium.
Calcium	A mineral needed for bones, teeth and blood clotting.
Iron	A mineral needed to make haemoglobin.
Collagen	A protein found in skin, hair, gums and bones.
Haemoglobin	The red pigment in red blood cells that binds oxygen.
Osteoporosis	A condition of weak, brittle bones.

Term	Meaning
Scurvy	A disease caused by severe vitamin C deficiency.
Rickets	A childhood disease of weak bones caused by vitamin D deficiency.
Anaemia	A condition caused by lack of iron that reduces haemoglobin.
Kwashiorkor	A disease caused by lack of protein.
Malnutrition	A diet with too little or too much of a nutrient or of energy.
DCPIP	A blue dye that is decolourised by vitamin C.

Section 26 of 26Exam technique

1

Saying water gives energy — water is needed but provides no energy.

2

Thinking a balanced diet means equal amounts of every food group — the proportions are different.

3

Saying lipids are only harmful — they are needed for insulation and energy storage.

4

Mixing up the functions of proteins and carbohydrates — proteins are for growth and repair.

1

Saying all people need the same diet — needs vary with age, activity, pregnancy and breastfeeding.

2

Saying vitamin D is made from calcium — vitamin D helps calcium to be absorbed.

3

Saying iron is used to make white blood cells — iron is used for haemoglobin in red blood cells.

4

Forgetting sunlight as a source of vitamin D — the skin makes it.

1

Saying scurvy is caused by vitamin D — scurvy is lack of vitamin C and rickets is lack of vitamin D.

2

Saying rickets affects only adults — it is a condition of children.

3

Forgetting that sunlight helps prevent rickets — the skin makes vitamin D.

4

Saying the energy value found by burning food is exact — heat loss makes it an underestimate.