Nutrition (Edexcel IGCSE Science (Double Award): Biology): Flashcards

In photosynthesis, light energy is absorbed by chlorophyll, the green pigment inside chloroplasts.

The waste product made and released during photosynthesis is oxygen.

• A source of energy in respiration

• Converted to starch for storage

• Used to synthesise lipids as an energy source in seeds

• Converted to cellulose to make cell walls

• Used to produce amino acids, when combined with nitrogen and other mineral ions

Starch.

Nitrogen and other mineral ions, absorbed by the roots.

Cellulose.

Something present in the environment in such short supply that it restricts life processes.

• Temperature

• Light intensity

• Carbon dioxide concentration

The amount a plant needs for photosynthesis is very small compared with the amount it takes up, so there is hardly ever too little water for photosynthesis.

Particles gain more kinetic energy, so successful collisions between reactants and enzymes become more likely and more products form.

The enzymes controlling photosynthesis become denatured — the active site changes shape and is no longer complementary to its substrate.

False.

At low temperatures the particles simply have less kinetic energy, so there are fewer successful collisions. The enzymes are not denatured.

The more light a plant receives, the faster the rate — until some other required factor is in short supply and becomes the limiting factor.

Carbon dioxide is a raw material, so the more present, the faster the reaction — until another factor becomes limiting.

The more chloroplasts, the more chlorophyll there is to absorb light energy, so the faster the rate of photosynthesis.

• Diseases, such as tobacco mosaic virus

• Lack of nutrients, such as magnesium

• Loss of leaves — fewer leaves means fewer chloroplasts

• Genetic factors, such as having variegated leaves

A plant's rate of photosynthesis is limited by whichever required factor is lowest at that time.

A magnesium-deficient plant photosynthesises slowly because it cannot make enough chlorophyll.

Where the line is rising, the factor on the x-axis is limiting.

Where the line is horizontal, something other than the x-axis factor is limiting.

False.

A horizontal line means light intensity is no longer limiting — something else, such as temperature or carbon dioxide concentration, has become the limiting factor.

Because a plant does not have unlimited supplies of its raw materials, so whichever factor is lowest restricts the rate.

It is a protective layer on the upper and lower sides of the leaf that prevents water loss.

It is thin, so it protects the leaf without blocking sunlight.

To allow light to pass through to the palisade mesophyll layer underneath it.

Column-shaped cells, tightly packed with chloroplasts, sitting at the top of the leaf so light hits the chloroplasts directly.

It contains internal air spaces that give a large surface area, so carbon dioxide can diffuse quickly to the photosynthesising cells.

• Guard cells

• Stomata

They absorb and lose water to open and close the stomata, controlling how much carbon dioxide enters the leaf for photosynthesis.

They are pores that let carbon dioxide diffuse into the leaf for photosynthesis, and let the oxygen produced diffuse out.

They support the leaf, holding it flat and spread out to catch light, and the xylem inside them delivers the water needed for photosynthesis.

• Xylem

• Phloem

Together they transport substances to and from the leaf.

Water, which the mesophyll cells use in photosynthesis.

Sucrose and amino acids around the plant.

To increase the area for absorbing light and for the diffusion of carbon dioxide.

So that carbon dioxide can diffuse quickly to the palisade mesophyll cells.

Magnesium ions are needed by the leaf to make chlorophyll.

The palisade mesophyll cells are tightly packed with chloroplasts to absorb more light.

False.

It lies just below the upper epidermis, at the top of the leaf, where the light is strongest.

False.

The cuticle is thin, so it protects the leaf and prevents water loss without blocking sunlight.

Photosynthesis provides carbohydrates, but plants also need proteins and chlorophyll.

Plants do not eat, so they must make these themselves — and that needs mineral ions from the soil.

Making chlorophyll.

Making amino acids, which are used to build proteins.

They are actively absorbed from the soil by the roots, then carried up the plant in the xylem.

False.

Mineral ions are taken in by active transport — they are moved against a concentration gradient, which requires energy.

Carbohydrates contain only carbon, hydrogen and oxygen.

Proteins contain nitrogen as well, and certain amino acids contain other elements too.

Magnesium ions are needed by a plant to make chlorophyll.

Nitrate ions are needed by a plant to make amino acids.

The plant cannot make enough chlorophyll, so its leaves turn yellow and its rate of photosynthesis falls.

The plant cannot make enough amino acids, and so not enough protein, which leads to poor, stunted growth.

Any naturally occurring inorganic substance.

True.

Without a source of these two mineral ions, a plant cannot photosynthesise or grow properly.

Submerge a bundle of pondweed such as Elodea in a beaker of water beneath an upturned funnel, with a water-filled boiling tube over the funnel's end.

As photosynthesis occurs, bubbles of oxygen collect in the tube and displace the water.

It relights a glowing splint.

By measuring the number of bubbles or the volume of oxygen produced in a set amount of time.

The glucose made is quickly used up, converted into other substances, transported or stored as starch.

Starch is stored in the chloroplasts, so testing for it reliably shows which parts of the leaf were photosynthesising.

Placing it in a dark cupboard for 24 hours means any starch already in the leaves is used up, so it cannot affect the results.

Drop the leaf into just-boiled water for 5 minutes.

Transfer it to a boiling tube of ethanol in a hot water bath for 5–10 minutes.

Rinse it in warm water.

Spread it on a white tile and cover it with iodine solution.

It denatures the enzymes and softens the leaf.

To remove the chlorophyll, so the colour change from iodine can be seen clearly.

To soften the leaf tissue again after it has been in ethanol.

False.

Ethanol is extremely flammable. Heat it in an electric water bath, or a beaker of water boiled in a kettle, and keep it away from naked flames.

De-starch the plant, partially cover a leaf with aluminium foil, and leave the plant in sunlight for a day.

Then remove the leaf and test it for starch.

The area that was covered stays yellow-brown — it could not photosynthesise, so no starch was made.

The area exposed to light turns blue-black.

De-starch the plant, then enclose one leaf in a conical flask containing potassium hydroxide and another in a flask without it as a control.

Leave in bright light for several hours, then test both leaves for starch.

It absorbs carbon dioxide from the air surrounding the enclosed leaf.

The leaf in the flask with potassium hydroxide stays orange-brown — no carbon dioxide, so no photosynthesis.

The control leaf turns blue-black.

Test a variegated leaf — one that is partly green and partly white — for starch.

Only the areas that contained chlorophyll stain blue-black.

The white areas stay orange-brown, because no photosynthesis occurred there and so no starch was stored.

A leaf that has been photosynthesising turns blue-black when iodine solution is added.

A diet that contains all of the food groups in the correct proportions.

• Carbohydrates

• Proteins

• Lipids

• Dietary fibre

• Vitamins

• Minerals (mineral ions)

• Water

The condition that results from an unbalanced diet, which can cause a variety of health problems.

Function: a source of energy.

Sources: bread, cereals, pasta, rice, potatoes.

Function: growth and repair.

Sources: meat, fish, eggs, pulses, nuts.

Function: insulation and energy storage.

Sources: butter, oil, nuts.

Function: provides bulk (roughage) for the intestine to push food through it.

Sources: vegetables, whole grains.

So that chemical reactions can take place in the body.

Sources: water, juice, milk, fruit and vegetables.

They are needed in small quantities to maintain health.

Sources: fruits and vegetables, meats, dairy products.

Strong teeth and bones.

Found in milk, cheese and eggs.

• Carbohydrate, the main and most readily used source

• Lipid, which stores energy and releases more per gram

It helps the body absorb calcium and is required for strong bones and teeth.

Found in oily fish and dairy products, and also made by the body in sunlight.

False.

It is found in oily fish and dairy products, but it is also made naturally by the body in sunlight.

• Oily fish

• Dairy products

It is also made by the body in sunlight.

Healthy skin, gums and connective tissue.

Found in citrus fruits and some green vegetables.

To make the pigment in the retina used for vision.

Found in meat, liver, dairy, leafy green vegetables and eggs.

To make haemoglobin, the pigment in red blood cells that helps carry oxygen.

Found in red meat, liver and leafy green vegetables.

Iron is needed in the diet to make haemoglobin, the pigment that carries oxygen in red blood cells.

Dietary fibre provides the roughage that intestinal muscles push against.

They increase towards adulthood, because energy is needed for growth, then decrease as adults get older.

Children also need a higher proportion of protein than adults, for growth.

Their muscles contract more and therefore respire faster, so more energy is needed for movement.

Energy is needed to support the growth of the developing fetus and the larger mass the mother carries.

Extra calcium and iron are also needed, to build the fetus's bones, teeth and blood.

The process in which relatively large, insoluble molecules in food are broken down into smaller, soluble molecules that can be absorbed into the bloodstream.

The passage through which food flows through the body, starting at the mouth and ending at the anus. Digestion occurs within it.

Accessory organs produce substances needed for digestion, such as enzymes and bile, but food does not pass directly through them.

• To provide cells with energy, via respiration

• As materials to build other molecules, for growth, repair and normal function

Mechanical digestion — the teeth chew food into smaller pieces, increasing its surface area to volume ratio.

Chemical digestion — amylase in saliva starts digesting starch into maltose.

The food is shaped into a bolus and lubricated by saliva so it can be swallowed.

It is the tube connecting the mouth to the stomach.

Wave-like contractions push the bolus down, without relying on gravity.

Mechanical digestion by churning, while protease enzymes begin chemically digesting proteins.

• Kills bacteria in food

• Provides the optimum pH for protease enzymes to work

It is the first section of the small intestine, where digestion of food leaving the stomach is completed by enzymes in the duodenum lining and enzymes secreted by the pancreas.

It is the second section of the small intestine, where water and digested food molecules are absorbed.

It is long and lined with villi to increase the surface area for absorption.

Slightly alkaline, around pH 8–9.

• Colon — water is absorbed from the remaining material to produce faeces

• Rectum — faeces are stored before leaving the body via the anus

It produces all three types of digestive enzyme — amylase, protease and lipase — and secretes them in an alkaline fluid into the duodenum.

The alkaline fluid raises the pH of the fluid leaving the stomach.

• Breaks down excess amino acids that are not used to make proteins, producing urea

• Produces bile, which emulsifies lipids

It stores bile, ready to release into the duodenum.

In the mouth, food is shaped into a ball called a bolus so it can be swallowed easily.

Water is absorbed from the remaining material in the colon to produce faeces.

False.

The pancreas is an accessory organ. Food does not pass through it, but it produces digestive enzymes that are released into the small intestine.

False.

Wave-like contractions of the muscles in its wall push the bolus down, so swallowing works in any position.

The wave-like contractions of muscles in the wall of the alimentary canal that move food along it.

• Circular muscles

• Longitudinal muscles

They reduce the diameter of the lumen of the oesophagus or small intestine.

They reduce the length of that section of the oesophagus or small intestine.

It continually lubricates the food mass and reduces friction.

It provides the roughage that the muscles need something to push against.

It is churned into a less solid form called chyme, which then continues on to the small intestine.

Muscles in the walls of the oesophagus create waves of contractions that force the bolus along.

In the stomach the bolus is churned into a less solid form called chyme.

False.

Peristalsis moves food along the whole alimentary canal, including the small intestine, not just the oesophagus.

True.

Mucus is produced continually to lubricate the food mass.

It mixes food with enzymes as well as keeping food moving along the alimentary canal.

To break down large, insoluble molecules into smaller, soluble molecules that can be absorbed into the bloodstream.

Chewing, churning and emulsification break large pieces of food into smaller ones, which increases the surface area for enzymes to work on.

The bonds holding large molecules together are broken, making smaller and smaller molecules. It is controlled by enzymes.

• Carbohydrases

• Proteases

• Lipases

It breaks down starch into maltose.

• The salivary glands

• The pancreas

• The small intestine

Salivary amylase is denatured by acid in the stomach; pancreatic amylase acts in the small intestine.

It breaks down maltose into glucose.

It is made in the small intestine, which is also where it acts.

• Amylase — starch to maltose

• Maltase — maltose to glucose

They break down proteins into amino acids.

Starch is a large, insoluble molecule.

It must be broken down to glucose, which is small and soluble enough to pass into the blood.

The stomach, the pancreas and the small intestine.

They break proteins down into amino acids.

They break down lipids into glycerol and fatty acids.

It is produced in the pancreas and secreted into the small intestine, where it acts.

Amylase breaks down starch into maltose.

Lipases break down lipids into glycerol and fatty acids.

False.

Amylase produced by the salivary glands is denatured by the acid in the stomach.

True.

It makes amylase, protease and lipase, and secretes them into the small intestine.

• Produced by cells in the liver

• Stored in the gall bladder, before release into the small intestine

Alkaline.

• Neutralising the hydrochloric acid from the stomach

• Emulsifying lipids — breaking large drops of fat into smaller ones

Because enzymes in the small intestine have a higher, more alkaline optimum pH than those in the stomach.

The breaking apart of large drops of lipid into smaller ones, which increases their surface area.

The more alkaline conditions and the larger surface area created by emulsification let lipase break lipids into glycerol and fatty acids more quickly.

The duodenum, the first part of the small intestine.

Because breaking a lipid drop into smaller drops does not break bonds or change the chemical structure of the molecules — which is what chemical digestion means.

Bile is produced by the liver and stored in the gall bladder.

Bile neutralises hydrochloric acid from the stomach so that intestinal enzymes can work.

False.

Bile is an alkaline substance containing bile salts. It emulsifies lipids mechanically — it does not catalyse a reaction.

False.

Bile is produced in the liver. The gall bladder only stores it.

The movement of small digested food molecules from the digestive system into the blood (glucose and amino acids) and the lymph (fatty acids and glycerol).

• Diffusion

• Sometimes active transport

By osmosis, primarily in the small intestine but also in the large intestine.

• It is very long

• Its surface is highly folded, with millions of villi

Both massively increase the surface area for absorption.

A tiny, finger-like projection on the folded inner surface of the small intestine that increases the surface area for absorption.

They sit on the surface of each villus and further increase the surface area available for absorption.

Because the wall of a villus is only one cell thick.

Each villus has a network of blood capillaries that continually transports glucose and amino acids away from the small intestine.

It is a lymph vessel running through the centre of the villus that transports fatty acids and glycerol away from the small intestine in the lymph.

• Enzymes produced in their walls assist with chemical digestion

• Their movement helps move food along and mix it with the enzymes present

It mixes food with enzymes and keeps material moving along the alimentary canal.

The wall of a villus is only one cell thick, which shortens the diffusion distance.

Fatty acids and glycerol are absorbed into the lymph rather than directly into the blood.

False.

Water is absorbed primarily in the small intestine, but also in the large intestine.

True.

They pass into the blood capillaries of the villi, while fatty acids and glycerol pass into the lacteal.