Exchange - Yr 1

Question 1

Surface area: volume ratio

Answer 1

The important relationship between the surface area of a biological unit such as a cell or a whole animal, and its overall volume, which affects many aspects of its biochemistry. As the size of the unit increases, its surface area grows relatively more slowly than its volume.

Question 2

Exchange surface

Answer 2

Surfaces across which substances could be transferred. To allow exchange to be efficient, surfaces will often have a large surface area:volume ratio, be very thin and selectively permeable. There will also often be movement of the environmental medium and a transport system to ensure the movement of the internal medium.

Question 3

Concentration gradient

Answer 3

The difference between the concentration of a gas or substance inside and outside of the cell. The steeper the concentration gradient, the faster the rate of diffusion.

Question 4

Tracheae

Answer 4

A large internal network of tubes in insects with supported rings to prevent them collapsing.

Question 5

Tracheoles

Answer 5

These tubes extend from the tracheae and extend throughout all the body tissues of the insect to allow atmospheric air to be brought directly to respiring tissues.

Question 6

Spiracle

Answer 6

Tiny pores that allow gases to enter and leave the tracheae (and water vapour to leave as well). They are opened and closed by a valve.

Question 7

Gill

Answer 7

Located within the body of the fish, behind the head.

Question 8

Gill filaments

Answer 8

Make up the gills of a fish – they are stacked up in a pile.

Question 9

Gill lamellae

Answer 9

At right angle to gill filaments, which increase the surface area of the gills.

Question 10

Countercurrent flow

Answer 10

Describes how the flow of water over the fill lamellae and the flow of blood within them are in opposite directions. Allows a diffusion gradient to be maintained all the way across the gill lamellae.

Question 11

Stomata

Answer 11

Minute pores that occur mainly on the leaves, especially on the underside. They allow gaseous exchange (and water vapour to leave as well). They are opened and closed by guard cells.

Question 12

Guard cells

Answer 12

Control the opening and closing of stomata.

Question 13

Spongy mesophyll

Answer 13

Tissue in the leaf, which has large air spaces so gases can readily come into contact with mesophyll cells and large surface area of mesophyll cells for rapid diffusion.

Question 14

Xerophyte

Answer 14

Plants which have a restricted supply of water which have evolved a range of adaptations to limit water loss through transpiration.

Question 15

Lungs

Answer 15

A pair of lobe structures made up of a series of highly branched tubules called bronchioles, which end in tiny air sacs called alveoli.

Question 16

Ventilation

Answer 16

The process in which air is constantly moved in and out of the lungs to maintain diffusion of gases across the alveolar epithelium. Also known as breathing.

Question 17

Trachea

Answer 17

A flexible airway that is supported by rings of cartilage which prevent it collapsing as the air pressure inside falls when breathing in. Its walls are made up of muscle, lined with ciliated epithelium and goblet cells.

Question 18

Bronchi

Answer 18

Two divisions of the trachea each leading to one lung. Amount of cartilage reduces as they get smaller. Also produce mucus to trap dirt particles and cilia that move this towards the throat.

Question 19

Bronchioles

Answer 19

A series of branching subdivisions of the bronchi whose walls are made up of muscle (which constricts to control the flow of air in and out of the alveoli) lined with epithelial cells.

Question 20

Alveoli

Answer 20

Minute air-sacs with a diameter of between 100µm and 300µm at the end of the bronchioles. They are lined with epithelium. Between the alveoli there are some collagen and elastic fibres.

Question 21

Inspiration

Answer 21

An active process when external intercostal muscles contract, internal intercostal muscles relax, ribs are pulled upwards and outwards and the diaphragm muscles contract causing it to flatten, increasing the volume of the thorax, which reduces the pressure.

Question 22

Expiration

Answer 22

A largely passive process when external intercostal muscles relax, internal intercostal muscles contract, ribs move downwards and inwards and the diaphragm muscles relax, decreasing the volume of the thorax, which increases the pressure.

Question 23

Diaphragm

Answer 23

A sheet of muscle that separates the thorax from the abdomen.

Question 24

Rib cage

Answer 24

the bony frame formed by the ribs round the chest

Question 25

Intercostal muscles

Answer 25

Lie between the ribs. Two sets – internal whose contraction leads to expiration and external whose contraction leads to inspiration.

Question 26

Enzyme

Answer 26

A protein that acts as a catalyst and so lowers the activation energy needed for a reaction.

Question 27

Absorption

Answer 27

Movement of digested food molecules through the wall of the intestine into the blood or lymph

Question 28

Oesophagus

Answer 28

Muscular tube which carries food from the mouth to the stomach

Question 29

Stomach

Answer 29

A muscular sac with an inner layer that produces enzymes. Its role is so store and digest food, especially proteins.

Question 30

Ileum

Answer 30

A long muscular tube where food is further digested. Enzymes are produced by its walls and by glands that pour their secretions into it. Inner walls are folded into villi which gives them a large surface area. Where products of digestion are absorbed into the bloodstream.

Question 31

Large intestine

Answer 31

Where water is absorbed.

Question 32

Rectum

Answer 32

The final section of the intestines where the faeces is stored before being egested by the anus.

Question 33

Salivary glands

Answer 33

Situated near the mouth. They pass their secretions via a duct into the mouth which contain salivary amylase which hydrolyses starch into maltose.

Question 34

Pancreas

Answer 34

A large gland situated below the stomach. It produces a secretion called pancreatic juice, which contains proteases to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch.

Question 35

Hydrolysis

Answer 35

How digestive enzymes function – the splitting up of molecules by adding water to the chemical bonds that hold them together.

Question 36

Carbohydrases

Answer 36

Type of digestive enzyme which hydrolyse carbohydrates, ultimately to monosaccharides.

Question 37

Lipases

Answer 37

Type of digestive enzyme which hydrolyse lipids (fats and oils) into glycerol and fatty acids.

Question 38

Proteases

Answer 38

Type of digestive enzyme which hydrolyse proteins, ultimately into amino acids.

Question 39

Salivary amylase

Answer 39

Produced by the salivary glands and released into the mouth and starts hydrolysing starch in food to maltose.

Question 40

Pancreatic amylase

Answer 40

Produced by the pancreas and released into the small intestine where it continues the hydrolysis of starch to maltose.

Question 41

Maltase

Answer 41

Produced by the epithelial lining and is a membrane-bound disaccharidase which breaks down maltose into glucose.

Question 42

Membrane-bound disaccharidase

Answer 42

An enzyme which is not released into the lumen of the ileum but is part of the cell-surface membranes of the epithelial cells that line the ileum. E.g. maltase

Question 43

Sucrase

Answer 43

Produced by the epithelial lining and is a membrane-bound disaccharidase which breaks down sucrose into the monosaccharides glucose and fructose.

Question 44

Lactase

Answer 44

Produced by the epithelial lining and is a membrane-bound disaccharidase which breaks down lactose into the monosaccharides glucose and galactose.

Question 45

Bile salt

Answer 45

Produced by the liver and split up lipids into tiny droplets called micelles.

Question 46

Emulsification

Answer 46

The process by which lipids are split up into tiny droplets called micelles by bile salts, which are produced by the liver. It increases the surface area of the lipids so that the action of lipases is sped up.

Question 47

Micelles

Answer 47

Tiny structures (4-7nm in diameter) formed when monoglycerides and fatty acids remain in association with the bile salts that initially emulsified the lipid droplets. They break down as they come into contact with the epithelial cells lining the villi of the ileum and release the monoglycerides and fatty acids which diffuse across the cell membrane into the epithelial cells.

Question 48

Chylomicrons

Answer 48

A structure formed when triglycerides associate with cholesterol and lipoproteins, which are adapted for the transport of lipids. Start forming in the endoplasmic reticulum and continuing in the Golgi apparatus.

Question 49

Lacteals

Answer 49

Lymphatic capillaries that are found in the centre of each villus, where chylomicrons pass into and then enter the bloodstream.

Question 50

Exocytosis

Answer 50

The outward bulk transport of materials through the cell-surface membrane. How chylomicrons move out of the epithelial cells by this process.

Question 51

Endopeptidases

Answer 51

A type of protease which hydrolyses the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules.

Question 52

Exopeptidases

Answer 52

A type of protease which hydrolyses the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases. They progressively release dipeptides and single amino acids.

Question 53

Dipeptidases

Answer 53

A type of protease which hydrolyse the bond between the two amino acids of a dipeptide. Dipeptidases are membrane-bound, being part of the cell-surface membrane of the epithelial cells lining the ileum.

Question 54

Lumen

Answer 54

The cavity of the intestines

Question 55

Villi

Answer 55

Folded finger-like projections of the ileum wall, about 1mm long, which are increase the surface area of the ileum and therefore accelerate the rate of absorption.

Question 56

Microvilli

Answer 56

Tiny finger-like projections from the cell-surface membrane of some animal cells.