Exchange

Question 1

What happens to surface area to volume ratio as a cell becomes bigger

Answer 1

the ratio decreases because the volume increases at a greater rate than the surface area

Question 2

Why is cell size limited

Answer 2

if a cell gets to big, molecules wont be able to enter and exit the cell quick enough for the cells needs

Question 3

What are features of a specialised exchange surface

Answer 3

• short diffusion distance
• large surface area to volume ratio
• maintaining a constant concentration gradient e.g. blood flow

Question 4

What is Fick’s law

Answer 4

(surface area X difference on concentration)/diffusion distance

Question 5

How are single-celled organisms adapter for efficient gas exchange

Answer 5

as they are single celled they have a short diffusion distance and a large surface area to volume ratio

Question 6

How is an insect adapted fo efficient gas exchange

Answer 6

• they have many spiracles which increases surface area
• oxygen goes in from a high to low oxygen concentration, through the tracheae then through the tracheoles by mass transport (contractions of muscles)
• then directly into the respiring tissues of the insect

Question 7

How does anaerobic respiration in insects lead to more efficient gas exchange

Answer 7

• water moves in to the cells from a high to low water potential by osmosis from the tracheoles
• this increases the surface area of tracheole, which shortens the diffusion distance for oxygen to diffuse into cell more efficiently

Question 8

How are fish adapted for efficient gas exchange

Answer 8

• they have many gills which have many gill filaments which increases surface area for diffusion
• on the gill filaments are gill lamellae which further increase the surface area and have a short diffusion distance
• gill lamellae have capillaries on them to maintain a concentration oxygen concentration gradient

Question 9

What is the counter current system in fish gills

Answer 9

• the flow of blood in the capillaries of the gill lamellae runs in the opposite direction to the water
• thus the deoxygenated blood is exposed to the water and gets oxygenated
• the oxygenated blood flows to respiring tissues and maintains a concentration gradient along the whole gill

Question 10

How is a leaf adapted for efficient gas exchange

Answer 10

• cuticle reduces water loss
• they’re many stomata which increases surface area for diffusion
• other cells are located close to the stomata which shortens diffusion distance
• large surface area of mesophyll cells for rapid diffusion
• guard cells can reduce the loss of gas and water vapour

Question 11

Why does CO2 diffuse into the leaf during the day and out during the night

Answer 11

during the day:
-CO2 is being used and taken in for photosynthesis

during the night:
-photosynthesis doesn’t take place at night and plants are constantly respiring which releases CO2

Question 12

How does an insect limit water loss

Answer 12

• as they have a small surface area to volume ratio it minimises the area which water is lost by diffusion
• they have a water proof exoskeleton so no water is lost
• the spiracles can be closed to reduce water loss

Question 13

What is an xerophyte

Answer 13

a type of plant that has adapted to reduce water loss by transpiration

Question 14

How are xerophytes adapted for limiting water loss

Answer 14

• a thick waxy cuticle which reduces water loss
• they can roll up there leaves so still air is trapped in the leaf which becomes water vapour that cam be reabsorbed by osmosis
• hairy leaves can can trap a layer of moist air to the leaf surface

Question 15

Why do humans need lungs and what is the process of gas exchange in humans

Answer 15

• humans need oxygen for respiration and high metabolic rate
• oxygen moves from a high to low concentration from the air, down the trachea, bronchi and bronchioles, into the alveoli of the lungs

Question 16

How are alveoli adapted for efficient gas exchange

Answer 16

• they are lined with epithelial cells that shorten the diffusion distance
• they have a network of capillaries that slow the flow of blood allowing more time for diffusion and to maintain a concentration gradient

Question 17

What is ventilation

Answer 17

where gases are constantly moved in and out of the lungs across the alveolar epithelium

Question 18

What is the process of inspiration

Answer 18

breathing in is a active process

• external intercostal muscles contract
• ribs are pulled up and out
• diaphragm contracts and flattens increasing volume of the thorax
• atmospheric pressure is greater than pulmonary pressure thus air forced into the lungs

Question 19

What is the process of expiration

Answer 19

breathing out is a passive process

• internal intercostal muscles contract
• ribs move down and in deceasing volume of thorax
• diaphragm relaxes and returns to size and further deceases volume of the thorax
• pulmonary pressure is greater than the atmospheric pressure thus air forced out the lungs

Question 20

How do you calculate pulmonary ventilation

Answer 20

pulmonary ventilation = tidal volume X ventilation rate

Question 21

What are risk factors that can lead to lung disease

Answer 21

• smoking
• genetic makeup
• air pollution

Question 22

Define digestion

Answer 22

mechanical and chemical breakdown of large molecules to small soluble molecules

Question 23

What are the main parts of the digestive system

Answer 23

salivary glads - release salivary amylase
oesophagus - moves food from mouth to stomach
stomach - contains optimum pH for amylase
small intestine (ileum) - absorption of nutrients and molecules from the food e.g. glucose
large intestine (colon) - absorption of water
rectum - final section where faeces is stored before removed via the anus

Question 24

How and where are carbohydrates digested

Answer 24

• carbohydrase hydrolyses with an salivary and pancreatic amylase it into its disaccharides e.g. maltose
• alkaline salts are produced by the pancreas and intestine wall to neutralise the pH
• the epithelial lining produces disaccharidase maltase which further hydrolysed into its monosaccharides e.g. alpha-glucose

Question 25

How are fats (triglycerides) digested

Answer 25

• bile salts produced in the liver emulsify the fats into smaller droplets called micelles to increase surface area
• lipases produced in the pancreas hydrolyse the ester bonds between the monoglycerides and fatty acids
• these get absorbed through the microvilli of the small intestine and are transported to the endoplasmic reticulum to re-form into triglycerides and combine with cholesterol, proteins and phospholipids to form chylomicrons
• which enter the lacteals (lymphatic capillary) and get absorbed by the blood stream

Question 26

What are endopeptidases

Answer 26

hydrolyse the peptide bonds between the amino acids in the central region of a protein to form a series of peptide molecules

Question 27

What are Exopeptidases

Answer 27

hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules from endopeptidases

Question 28

What are dipeptitases

Answer 28

they are membrane bound enzymes that hydrolyse the bond between dipeptides

Question 29

How is glucose co-transported into the blood from the small intestine

Answer 29

• glucose is co-transported into the epithelial cells from the lumen by facilitated diffusion with sodium ions
• sodium is actively transported into the capillary through a sodium potassium pump
• potassium moves into the epithelial cell from the bloodstream to maintain concentration gradient
• glucose diffuses in by facilitated diffusion along side the sodium ion

Question 30

Explain the structure of the ileum related to function

Answer 30

squamous epithelial cells - short diffusion distance for efficient diffusion rate

microvilli - increases surface area and amount of proteins for increased diffusion

good blood supply - to maintain a constant concentration gradient