Exchange

Question 1

Adaptations to the insect exchange system to reduce water loss

Answer 1

Waterproof coverings over their body surfaces

Small SA:Volume to minimise the area of which water can be lost

Question 2

Due to insects small SA:Volume (to minimise the area of which water can be lost) they cannot use their body surface to diffuse respiratory gases, what is the solution ??

Answer 2

They have a system of tubes called the tracheal system to deliver oxygen to the tissues

Question 3

Spiracles

Answer 3

When spiracles are open, water can evaporate, so insects only periodically open them to allow gas exchange and limit water loss - spiracles also have hairs on them that catch water vapour

Question 4

Trachea

Answer 4

Supported by rings to stop them collapsing , trachea divide into smaller holes called tracheoles

Question 5

Along the diffusion gradient

Answer 5

Oxygen is used up by respiring cells

Concentration towards ends of tracheoles falls

Creates a concentration gradient

Oxygen diffuses from the atmosphere along the trachea and tracheoles to muscle cells

CO2 is produced by respiring cells, creates a concentration gradient in the opposite direction

Question 6

Mass transport

Answer 6

The spiracles close and muscles pull the skeletal plates of the abdomen together

This squeezes the tracheal system and pumps air in the sacs which speeds up gas exchange

Question 7

The ends of the tracheoles are fluid filled

(hint .. lactase & WP)

Answer 7

During major activity, muscle cells respire anaerobically which produces lactase (soluble and lowers WP of muscle cells)

Water moves in by osmosis

Water in ends of tracheoles decrease in volume & draws air in

Final diffusion pathway is air not liquid

Question 8

Describe how the insect gas exchange system provides cells with sufficient oxygen and limits water loss

Answer 8

Spiracles allow the diffusion of oxygen

Tracheoles are highly branched so large SA

Tracheole walls are permeable to oxygen

Chitin is impermeable so reduction of water loss

Spiracles can close so less water loss

Question 9

Gas exchange in the leaves of a plant during different intensities of light

Answer 9

Bright light = CO2 in , O2 out ( rate of photosynthesis > rate of respiration )

Dim light = No net exchange of gases ( rate of photosynthesis = rate of respiration )

No light = O2 in , CO2 out ( rate of photosynthesis < rate of respiration )

Question 10

Features of a lead allowing rapid diffusion of gases

Answer 10

• Thin, flat shape so short diffusion pathway and large SA

• Diffusion takes place in gas (air) so more rapid than in water

• Many stomata in lower epidermis so no cell is far from a stomata ( short diffusion pathway )

• Numerous interconnecting air spaces throughout the mesophyll so gases can easily come into contact with mesophyll cells

• Palisade and other mesophyll cells are elongated so large SA for rapid diffusion

Question 11

Structure of a leaf

Answer 11

Cuticle: Waxy later to prevent water loss from the leaf surface

Upper epidermis: Protects the internal tissues from mechanical damage, bacterial and fungal invasion

Palisade mesophyll: Many chloroplasts , cells closely packed together to efficiently absorb light

Spongey mesophyll: Irregular cells loosely packed together to leave numerous large air spaces to allow rapid diffusion of gases throughout the leaf

Stroma: Opening which allows gases to pass through in/out the leaf

Guard cells: Control the size of the stroma and close when plant is dehydrated

Question 12

Stomatal opening during day and night

Answer 12

Day: Stomata open - CO2 to move in, O2 out for photosynthesis

Night: Most stomata closed - plant isn’t photosynthesising , open enough for respiration

Question 13

Why would the plant close the stomata during the day?

Answer 13

Prevents excess water loss through transpiration (to conserve water) at the hottest point of the day

Question 14

Xerophyte adaptations

Answer 14

Thick cuticle: Waterproof barrier to reduce water loss e.g. holly

Rolled leaves: Stomata on lower epidermis, high water potential reduces water loss e.g. marram grass

Hairy leaves: Traps moody air next to leaf surface, water potential gradient is reduced so less water lost by evaporation e.g. heather plant

Stomata in pits: Traps moist air and reduces water potential gradient e.g. pine tree

Small SA:Volume ratio: Slower rate of diffusion, rate of water loss reduced e.g. spines of a cactus

Surface & deep roots: Maximise water uptake e.g. cacti

Question 15

Exchange between small organisms and their environment

Answer 15

SA large enough compared to volume to allow efficient exchange across their body surface

Question 16

Exchange between larger organisms and their environment

Answer 16

As organisms get larger, their volume increases at a faster rate than their SA, simple diffusion can no longer meet the needs of the organism, it would take too long for substances to dissolve

Question 17

Features of gas exchange surfaces

Answer 17

• Large SA:Volume ratio

• Very thin, flat shape so short diffusion pathway

• Selectively permeable, allows selected materials to cross

• Movement of the environmental medium e.g. air to maintain the diffusion gradient

• A transport system, ensures movement of internal medium e.g. blood to maintain the diffusion gradient which the gases can diffuse

Question 18

Gas exchange in fish : Movement of water in

Answer 18

Operculum closes

Mouth opens

Buccal cavity lowers - now has low pressure due to increased volume

Water enters

Question 19

Gas exchange in fish : Movement of water out

Answer 19

Operculum opens

Mouth closes

Buccal cavity rises - now has high pressure due to decreased volume

Water leaves

Question 20

Structure of lamellae

Answer 20

Many capillaries = good blood supply

Each full is covered in filaments = increased SA

Each filament = covered in lamellae

Lamellae = increased SA & are thin = short diffusion pathway

Question 21

Countercurrent flow mechanism

Answer 21

Capillaries carry blood in the opposite direction to the water

This maximises oxygen uptake and increases the efficiency of gas exchange

Also ensures a good diffusion gradient along the whole width of the gill lamellae

Question 22

In mammals, the volume of oxygen that has to be absorbed and the volume of carbon dioxide that must be removed are large, why?

Answer 22

They are relatively large animals/organisms with a large volume of living cells

They maintain a high body temperature which is related to them having high metabolic and respiratory rates

Question 23

The trachea in humans

Answer 23

A flexible airway that is supported by rings of cartilage

The cartilage prevents the trachea collapsing as the air pressure inside falls when breathing in

The tracheal walls are made up of muscle

Lined with ciliates epithelium and goblet cells

Question 24

The bronchi in humans

Answer 24

2 divisions of the trachea

Each leads to a lung

Similar in structure to trachea

Produce mucus to trap dirt

Have cilia to move the dirt mucus towards the throat

Question 25

The bronchioles in humans

Answer 25

Series of branching subdivisions of the bronchi Walls are made of muscle lined with epithelial cells - allows them to constrict so they can control the flow of air in and out the alveoli

Question 26

The alveoli in humans

Answer 26

Small air sacs at the end of the bronchioles Between the alveoli is collagen and elastic fibres Lined with epithelium Elastic fibres allow the alveoli to stretch as they fill with air while breathing in

Question 27

The mechanism of breathing

Answer 27

When the pressure of the atmosphere is greater than the air pressure inside the lungs, air is forced into the lungs (inhalation) When the air pressure inside the lungs is greater than that of the atmosphere, air is forced out of the lungs (exhalation)

Question 28

The pressure changes within the lungs are brought about by the movement of 3 sets of muscles…

Answer 28

The diaphragm, which is a sheet of muscle that separates the thorax from the abdomen The intercostal muscles, which lie between the ribs: • Internal intercostal muscles, whose contraction leads to exhalation • External intercostal muscles, whose contraction leads to inhalation

Question 29

Inspiration (Inhalation)

Answer 29

Breathing in is an ACTIVE process 1. The external intercostal muscles contract, while the internal intercostal muscles relax 2. The ribs are pulled upwards and outwards, increasing the volume of the thorax 3. The diaphragm muscles contract, causing it to flatten, which also increases the volume of the thorax 4. The increased volume of the thorax results in reduction of pressure in the lungs 5. Atmospheric pressure is now greater than pulmonary pressure, and so air is forced into the lungs

Question 30

Expiration (Exhalation)

Answer 30

Breathing out is a LARGELY PASSIVE PROCESS 1. The internal intercostal muscles contract, while the external intercostal muscles relax 2. The ribs move downwards and inwards, decreasing the volume of the thorax 3. The diaphragm muscles relax and so it is pushed up again by the contents of the abdomen that were compressed during inspiration. The volume of the thorax is further decreased 4. The decreased volume of the thorax increases the pressure in the lungs 5. The pulmonary pressure is now greater than that of the atmosphere and so air is forced out the lungs

Question 31

Carbohydrases..

Answer 31

Hydrolyse carbohydrates , to monosaccharides

Question 32

Lipases..

Answer 32

Hydrolyse lipids (fats and oils) into glycerol and fatty acids

Question 33

Proteases…

Answer 33

Hydrolyse proteins to amino acids

Question 34

Carbohydrate digestion

Answer 34

Salivary amylase hydrolyses the alternate glycosidic bonds of the starch molecule to produce the disaccharide maltose Stomach acid denatures the amylase and prevents further hydrolysis of the starch Pancreatic amylase continues the hydrolysis of starch to maltose The maltose is hydrolysed into the monosaccharide a-glucose by the enzyme maltase which is a membrane bound disaccharide

Question 35

Lipid digestion

Answer 35

Lipids are hydrolysed by enzymes called lipases Lipases hydrolyse the ester bonds found in triglycerides to form fatty acids and monoglycerides Lipids are are firstly split into micelles by bile salts which are produced by the liver This process is called emulsification which increases the SA of the lipids so that the action of lipases is speeded up

Question 36

Protein digestion

Answer 36

Proteins are hydrolysed by a group of enzymes called peptidases (proteases) • Endopeptidases hydrolyse the peptide bonds between amino acids in the central region of a protein molecule • Exopeptidases hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases - this releases dipeptides and single amino acids • Dipeptidases hydrolyse the bond between the two amino acids of a dipeptide -> dipeptidases are membrane-bound

Question 37

Where are digestive enzymes produced?

Answer 37

Salivary glands : Amylase Pancreas : Proteases , Amylase , Lipase

Question 38

Suggest why the stomach does not have villi or microvilli

Answer 38

Villi and microvilli increase SA to speed up the absorption of soluble molecules The food in the stomach has not yet been hydrolysed into soluble molecules so they cannot be abso Villi and microvilli would be unnecessary

Question 39

Absorption of amino acids and monosaccharides

Answer 39

Sodium ions actively transported out of epithelial cells by the sodium-potassium pump This maintains a higher concentration of sodium ions in the lumen of the intestine than in the epithelial cells Sodium ions diffuse into the epithelial cells down this concentration gradient They carry either amino acid molecules or glucose molecules into the cell with them The amino acids/glucose pass into the blood plasma by facilitated diffusion

Question 40

Absorption of triglycerides

Answer 40

Lipids are emulsified into micelles to increase the SA by bile salts The micelles come into contact with the epithelial cells lining the villi of the ileum Micelles break down and release monoglycerides and fatty acids (non-polar so diffuse across cell-surface membrane into epithelial cells) Monoglycerides and fatty acids transported to endoplasmic reticulum-> form triglycerides In the Golgi apparatus, they associate with cholesterol and lipoproteins to form chylomicrons Chylomicrons move out the epithelial cells by exocytosis