human nutrition

what is a balanced diet?

a diet that contains all the nutrients needed by the body in the correct proportions to maintain health

what are the components of a balanced diet?

carbohydrates, proteins, lipids, vitamins, minerals, water and dietary fibre

what are the sources and functions of carbohydrates?

bread, pasta, rice, potatoes, sugar

provides glucose, which is used in cellular respiration to release energy

what are the sources and functions of protein?

meat, fish, eggs, pulses, cheese

required for growth and repair of tissues

what are the sources and functions of lipids?

butter, oil, nuts, cheese

long term store of energy; insulation - reduces heat loss through the surface of the body; protects organs from mechanical damage

what are the sources and functions of vitamin A?

liver, orange fruit and veg: carrots, butternut squash, sweet potatoes, mangoes, apricots

required to make pigments found in retina cells in the eye; also protects surface of the eye

deficiency can cause night blindness

what are the sources and functions of vitamin C?

oranges, lemons, grapefruits, peppers, spinach

needed for making collagen, which helps maintain healthy connective tissue

deficiency can cause scurvy

what are the sources and functions of vitamin D?

oily fish, eggs, fortified foods such as milk and cereal products

helps with the absorption of calcium and so required for healthy bones and teeth

deficiency can cause rickets in children, and poor teeth

what are the sources and functions of calcium?

milk, cheese, yoghurt

needed for bone and teeth strength

deficiency can cause rickets in children

what are the sources and functions of iron?

red meat e.g. liver; spinach, kale

required for the production of haemoglobin and therefore the efficient transfer of oxygen

deficiency can cause anemia

what are the sources and functions of water?

drinking water, cucumber, tomatoes, oranges, melon

needed for cell reactions to take place; helps regulate body temperature through sweating

what are the sources and functions of dietary fibre?

spinach, cabbage, oats, barley

non digestible so provides bulk against which muscles of the digestive system can contract. Aids peristalsis.

deficiency can cause constipation

how does age affect energy requirements?

• children and teenagers need more energy for growth

• older adults may need less energy as growth has stopped and activity levels or muscle mass may be lower

how do activity levels affect energy requirements?

• more active people need more energy as their muscles contract more frequently, so they require more energy for movement

how does pregnancy affect activity levels?

• energy requirements will increase in order to support the growth of the fetus

• energy needs also increase due to the extra mass of the baby

what is the alimentary canal?

the alimentary canal is a continuous passage running from the mouth to the anus through which food travels

what is the function of the alimentary canal?

its function is to ingest food, digest food into small, soluble molecules, absorb digested nutrients into the blood, and egest undigested material from the body

what is the function of the mouth?

• mechanical digestion: teeth break up large food pieces into smaller pieces to increase the surface area to volume ratio (food bolus)

• salivary glands produce saliva to lubricate the food bolus so it can be swallowed easily

• salivary glands produce saliva, which contains amylase, which breaks down starch into glucose

what is the function of the oesophagus?

• it is a muscular tube connecting the mouth to the stomach

• it transports food bolus down the oesophagus and into the stomach through peristalsis

what is the function of the stomach?

• releases gastric juice from the stomach lining when it detects food in the stomach

• gastric juice is made up of pepsin, which breaks down proteins, and hydrochloric acid, which makes stomach acidic in order for pepsin to work and to kill any ingested bacteria

• its muscular walls perform peristaltic contractions that churn food, making it into smaller particles and forming a semi liquid mixture called chyme

what is the function of the duodenum?

the duodenum is the first part of the small intestine

• it receives chyme from the stomach and mixes it with bile

• carbohydrases, proteases and lipases digest food in the duodenum

• peristalsis occurs here to push the chyme forward to continue the digestive process

what is the function of the ileum?

the ileum is the part of the small intestine where most absorption of digested nutrients take place

• it absorbs glucose and amino acids into the blood capillaries

• fatty acids enter the intestinal lining before reaching the blood

• it absorbs digested soluble molecules into the blood

• it is lined with villi to maximise absorption

what is the function of the colon?

• it absorbs excess water and some mineral ions from the remaining gut contents

what is the function of the rectum?

the last part of the large intestine

• it stores faeces temporarily before they are removed from the body through the anus during egestion

what is the function of the pancreas?

• produces protease, amylase and lipase enzymes and secretes these into the small intestine

diagram of the digestive system

how is food moved through the gut?

Peristalsis - the wave-like contractions created by circular muscles and longitudinal muscles that squeeze food through the alimentary canal

what are digestive enzymes?

biological catalysts that speed up the chemical breakdown of large, insoluble food molecules into smaller, soluble molecules that can be absorbed

how are carbohydrates (starch) broken down?

broken down by carbohydrases (amylase and maltase)

starch → maltose by amylase

maltose → glucose by maltase

how are proteins broken down?

broken down by proteases in the stomach and small intestine

proteins → amino acids

how are lipids broken down?

broken down by lipases

lipids → glycerol + fatty acids

where is bile produced and stored?

the liver produces bile

the gallbladder stores bile

the duodenum receives bile from the gallbladder

what are the functions of bile?

• neutralises stomach acid - food leaving the stomach is acidic as it contains hydrochloric acid. bile is alkaline, so it neutralises the stomach acid and helps create the optimum pH for enzymes in the small intestine

• emulsifies large drops of fat. This increases the surface area which allows lipase to chemically break down the lipid into glycerol and fatty acids faster

what is absorption?

the movement of the products of digestion through the wall of the small intestine into the blood or lymph

how is the small intestine adapted for absorption?

It is lined with villi

villi have many adaptions to increase the rate of absorption:

• they have microvilli, which increases the surface area and therefore increases the diffusion of digested soluble molecules into the blood

• it has a thin epithelial layer, which reduces the distance molecules have to travel and therefore increases the absorption of all products of digestion

• it has mitochondria rich epithelial cells, which provide ATP for the active transport of glucose and amino acids

• it has a continuous blood flow, so glucose and amino acids can be transported away from the small intestine

• it has a dense capillary network, so glucose and amino acids can pass into the blood for transport around the body

• It has a lacteal, so glycerol and fatty acids can pass into the lymph for transport around the body

diagram of a villus

required practical - investigate the energy content of food

1) measure 20cm³ of water into a boiling tube

2) record the initial temperature of the water using a thermometer

3) record the initial mass of the food sample using a scale

4) secure the food on a mounted needle

5) ignite the food with a Bunsen burner and position it beneath the boiling tube at a fixed distance to heat the water

6) record the final temperature once the food stops burning

formula: energy transferred (J) = temperature increase (degrees C) x mass of water (g) x specific heat capacity of water (4.2)

experiment inaccuracies

Heat lost to the surroundings - Not all the energy heats the water - use insulation

Incomplete combustion - Some of the food's chemical energy is not released - Ensure the food burns as completely as possible

Food sample burns inconsistently - Results may not be comparable - Keep the distance between the food and container constant