organisms exchange substances with their environment

Question 1

why do multicellular organisms require specialised gas exchange surfaces?

Answer 1

they have a smaller surface area to volume ratio meaning that the distance needed to be crossed by diffusion is larger and substances cannot therefore easily enter the cells

Question 2

explain why a small mammal needs a relatively high metabolic rate compared to a large mammal

Answer 2

a small mammal has a bigger surface to volume ratio than a large mammal
this means that heat is lost more easily from the small mammal
so a mammal requires a relatively high metabolic rate in order to generate enough heat to maintain a constant body temperature

Question 3

what are three features of an efficient gas exchange surface?

Answer 3

-a large surface area
-thin walls to lead to short diffusion pathway
-steep concentration gradient which is maintained by a good blood supply or ventilation

Question 4

explain the process of gas exchange in an insects’ gas transport system.

Answer 4

-insects have a waterproof chitin exoskeleton that is impermeable to gases
-spiracles are pores on the body’s surface which open and close to allow gases to move in and out of the trachea by simple diffusion.
-oxygen travels down its diffusion gradient towards the respiring cells. the respiring cells use up oxygen which lowers the concentration gradient at the end of the tracheoles drawing more oxygen down its gradient
-the trachea tend to branch of into smaller tracheoles with thin permeable cell walls that allow oxygen to diffuse directly into the cells
-carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released to the atmosphere
–rings of muscle in the insects body contract and relax in a rhythmical abdominal pumping. the contraction f of the muscles can squeeze the trachea, enabling mass movement of air into and out

Question 5

adaptions of insects to water loss

Answer 5

-they have the ability to close their spiracles
-tiny hairs surround the spiracles
-they have a waxy cuticle

Question 6

explain the process of gas exchange in a fish

Answer 6

-oxygenated water enters the fish through its mouth and passes out through the gills
-each gill is made of lots of thin plates called gill filaments which give a big surface area for exchange of gases
- the gill filaments are covered in tiny structures called lamellae which create a larger surface area
-the counter current system means that blood flows through the lamellae in one direction and the water in flows in the opposite direction. this maintains a concentration gradient as the concentration of oxygen in the water is always higher than in the blood which maximised the amount of oxygen diffusing into the blood

Question 7

describe and explain how fish maintain a flow of water over the gills

Answer 7

-mouth opens and operculum shuts
-floor of the mouth is lowered
-mouth closes and operculum opens
-floor of the mouth is raised
-this causes and increased pressure which forces water over the gills

Question 8

define ventilation

Answer 8

movement of air into and out of the lungs

Question 9

define tidal volume

Answer 9

the volume of air we inspire and expire during each breath at rest

Question 10

define breathing rate

Answer 10

the number of breaths we take per minute

Question 11

define forced vital capacity

Answer 11

the maximum volume of air a person can breath out in a breath

Question 12

define forced expiratory volume

Answer 12

the maximum volume of air a person can expire in one second

Question 13

calculate the pulmonary ventilation rate?

Answer 13

PVR= tidal volume x breathing rate

Question 14

describe the function of the nasal cavity in the human gas exchange system.

Answer 14

the nasal cavity provides a good blood supply to warm and moisten the air entering the lungs. the goblet cells in the membrane secrete mucus which trap dust and bacteria to prevent it entering the lungs

Question 15

recall the structure of the trachea

Answer 15

• wall made of c shaped cartilage which creates flexibility
• cartilage is strong so trachea/bronchi do not collapse
• lining made of goblet cells and ciliated epithelial cells
• goblet cells make mucus , which traps pathogens/particles
• ciliated epithelial cells have cilia, which pushes mucus up and out of lungs

Question 16

describe the functions and adaptations of the alveoli in the human gas exchange system.

Answer 16

-squamous epithelium cells are one cell thick creating a short diffusion pathway which leads to faster diffusion
-good blood supply from the network of capillaries maintains a concentration gradient
-there a many alveoli which creates a large surface area to volume ratio for faster diffusion
-have moist mebrane that allows gases the dissolve in the moisture so they can diffuse
-permeable to gases
-elastic tissue allows it to recoil after expansion

Question 17

describe how the tracheal system is adapted for gas exchange

Answer 17

-thin tracheal walls so short diffusion distance from cells
-high branched tracheoles create large surface area and creates a shorter diffusion distance
-fluid moves out during exercise as there is a faster diffusion through air
-body can be moved to move air which maintains a concentration gradient

Question 18

Why is diffusion of gases between the alveoli and the blood very rapid?

Answer 18

1. the capillaries are narrow , hence the rbcs are slowed , allowing more time for diffusion
2. red blood cells are flattened against capillary walls, reducing the diffusion distance
3. the walls of both alveoli and capillaries are very thin, hence there’s a short diffusion distance
4. alveoli and pulmonary capillaries have a very large total surface area
5. ventilation of air in the lungs and circulation of blood maintains a steep concentration gradient
6. blood flow through the pulmonary capillaries maintain a concentration gradient

Question 19

explain inspiration process.

Answer 19

-external intercostal muscles contract which pulls the ribcage upwards and outwards
-internal intercostal muscles relax
-the diaphragm contracts causing it to flatten
-this increases the volume of the thoracic cavity
-air pressure inside the lungs is lower relative to the atmospheric air pressure so air moves into the lungs

Question 20

explain the expiration process.

Answer 20

-external intercostal muscles relax causing the ribcage to move downwards and inwards
-the internal intercostal muscles can contract
-the diaphragm relaxes causing it to dome upwards
-the volume of the thoracic cavity decreases
-air pressure inside the lungs is higher relative to the atmospheric air pressure so air moves out of the lungs.

Question 21

how does lung disease effect gas exhange?

Answer 21

thicker tissue in the alveoli increases the diffusion distance causing a slower rate of gas exchange
this means cells receive less oxygen so the rate of aerobic respiration reduced and less ATP is produced. this causes fatigue

Question 22

how does lung disease effect ventilation?

Answer 22

-reduced elasticity causes lungs to expand and recoil less causing a reduced tidal volume. for example in cystic fibrosis scar tissue builds up which is less elastic.
-narrower airways reduces the forced expiratory volume such as asthma where the bronchi are inflamed reducing the airways

Question 23

what occurs during an asthma attack

Answer 23

-smooth muscle in the bronchi contract
-increased production of mucus by the goblet cells
-diameter of the airways is reduced
-reduced flow of air

Question 24

describe a method to find the surface area of a leaf

Answer 24

-draw around a leaf on a piece of graph paper
count the number of squares
-multiply by 2 for the top and bottom of the leaf

Question 25

describe how a leaf is adapted to gas exchange?

Answer 25

-there are numerous air spaces within the spongy mesophyll layer which allows gases to move around the leaf
-many small pores called stomata on the underside of the leaves which creates a short diffusion pathway
-thin and flat to provide a short diffusion pathway and creates a large surface area to volume ratio for more rapid diffusion

Question 26

what are xerophytes?

Answer 26

plants that live in conditions which have limited freshwater

Question 27

what are some xerophytic features of plants?

Answer 27

-have hairs so to trap water vapour and decrease the water potential gradient
-stomata are in pits so to trap water vapour and decrease water potential gradient
-they have a thick waxy cuticle to reduce water loss by transpiration or evaporation as it increases the diffusion distance
-has rolled leaves so to trap water vapour and decrease the water potential gradient

Question 28

explain why the rate of water uptake in a plant might not be the same as the rate of transpiration.

Answer 28

-water is used for support as it maintains the plants turgidity
-water is used in the photosynthesis process
-water is produced during respiration

Question 29

define digestion.

Answer 29

hydrolysis of large insoluble substances into smaller soluble substances

Question 30

describe and explain features which you would expect a specialised cell to have for absorption.

Answer 30

-microvilli so to create a large surface area for absorption
-large amount of carrier proteins present for active transport
-large amount of channel proteins for facilitated diffusion so to speed up the rate of absorption
-larger number of mitochondria for aerobic respiration which will produce more ATP as an energy source

Question 31

where is maltase produced and what its function?

Answer 31

maltase is produced in the small intestines and pancreas
maltose breaks down maltose into glucose

Question 32

where is amylase produced and what is its function?

Answer 32

-produced in the salivary glands, the pancreas and the small intestine
-it hydrolyses polysaccharide starch into maltose by hydrolysing the glycosidic bonds

Question 33

describe how proteins are digested in the human gut?

Answer 33

-hydrolysis of peptide bonds
-endopeptidases break the peptide bonds between specific amino acids in the middle of the polypeptide to break polypeptides into smaller chains
-exopeptidases break bonds between terminal amino acids to remove specific amino acids from the proteins
-membrane-bound dipeptidases break dipeptides into amino acids by hydrolysing the peptide bond

Question 34

explain how sodium ions are involved in co transport

Answer 34

-sodium ion are actively transported out the small intestine epithelium cells into the bloodstream
-this maintains a concentration gradient by maintaining a higher concentration of sodium ions in the small intestine lumen than the epithelial cells
-this causes sodium ions to move down their conc gradient into the epithelium cells by facilitated diffusion
-glucose is absorbed with the sodium ions via a sodium-glucose co- transporter protein

Question 35

what is the role of lipases?

Answer 35

-lipases are enzymes that catalyse the break down of lipids into monoglycerides and fatty acids
-the ester bonds in the lipids are hydrolysed

Question 36

describe how triglycerides are digested

Answer 36

-bile salts cause the emulsification of lipids into smaller droplets to increase the surface area for lipase action
-lipase hydrolyses the ester bonds in the triglycerides to form fatty acids and monoglycerides
-there is further emulsification and hydrolysis of triglycerides to form micelles. micelles transport the monoglycerides and fatty acids to the epithelial cells
-when the micelles come into contact with the epithelial cell they breakdown and release the monoglycerides and fatty acids which which cross the cell surface membrane by simple diffusion
-once inside the cell, triglycerides are made from them at the endoplasmic reticulum
-the triglycerides combine with proteins, lipoproteins and cholesterol to form chylomicrons