Exchange And Transport Systems: - Size And Surface Area.

- Size And Surface Area - 

Every organism's needs to be able to exchange substances or molecules with its environment in order to sustain life.

For example, Humans exchanges oxygen and carbon dioxide with its environment.

Cells need to take in oxygen (for aerobic respiration) and nutrients. // Also need to excrete (get rid of) waste products i.e. carbon dioxide and urea // heat needs to be exchanged so that the organism can maintain a constant temperature.


Smaller animals have a higher surface area : volume ratios

A mouse has a much larger surface area : volume ratio compared to an elephant.

However they are unable to perform exchange via their surface.

Although some mammals or other organisms have a large surface area to volume ratio, they are multi-cellular which means that they have a large diffusion distance and high demand as well as this they have a specialised exchange and transport system. They also have impermeable surface - this is to prevent pathogens entering and reducing water loss.

The exchange system would mean that the increases rate of diffusion of nutrients in and wastes out and the transport system had delivered nutrients and remove waste from all cells.


Animals with a high surface area : volume ratio tend to lose more water as it evapourates from their surface // small animals living in the desert would have kidney structure adapted to producing less urine to compensate for the loss of water.

High metabolic rates // small animals in the cold regions would have to eat large amount of high energy foods to maintain the amount of energy they use.

Large animals are adapted to extreme hot conditions // elephants have large flat ears to increase their surface area allowing them to lose more heat // hippos have behavioral adaptations to spend much of their day in water which helps them lose heat.

Exchange And Transport Systems: - Exchange Of Gases In The Lungs

- Exchange Of Gases In The Lung - 

Role of the alveoli in gas exchange 

Epithelial cells // alveolus is a network of pulmonary capillaries // narrow // red blood cells are flatterned against the thin capillary walls in order to squeeze through.

Diffusion of gases between the alveoli and the blood will be very rapid.


Red blood cells slow down passing through pulmonary capillaries allowing more time for diffusion.

Distance between the alveolar air and red blood cells is reduced as red bloods are flattened against the walls of the capillaries.

Alveoli and capillaries are very thin = short diffusion pathways // made of specialised squamous cells

Exchange And Transport Systems: - Mechanisms Of Breathing.

- Mechanisms Of Breathing - 

There is two types of ventilation 

Inspiration = Active process - requires energy 

External intercostal muscle - Contracts 

Internal intercostal muscle - Relax 

Ribs - Upwards and outwards 

Thoracic cavity - Increases in volume 

Diaphragm - Contract 

Expiration = Passive process - does not require 

External intercostal muscle - Relaxes 

Internal intercostal muscle - Contracts

Ribs - Downwards and inwards 

Thoracic cavity - Decreases in volume 

Diaphragm - Relaxes 

Movement of the intercostal muscles = antagonistic - opposing. 

Exchange And Transport Systems: - Structure Of The Human Gas-Exchange System

- Structure Of The Human Gas-Exchange System - 

Mammalian lung:

Lungs are site of gas exchange in mammals 

They are in the body as the air is not dense to support and protect 

Body as whole would otherwise lose a great deal of water and dry out. 

Lungs are specialised for gas exchange:

When you breath in air this travels down the Trachea // windpipe.

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Bronchi/Bronchus is the split of the trachea at the end of the wind pipe. 

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Bronchioles is the further branching of the bronchi into smaller tubes. 

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Alveoli are at the end of the bronchioles which are 'air sacs'. 

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The rib-cage, intercostal muscles and diaphragm all work together to move air in and out. 

Exchange And Transport Systems: - Limiting Water Loss

- Limiting Water Loss - 

Limiting water loss in insects 

Insects have evolved the following adaptations:

- Small surface area to volume ratio = minimise area over which water is loss 

- Waterproofing covering = outer skeleton of chitin is covered with waterproof cuticle.

- Spiracles = opening of the tracheae at the body surface can be closed due to water loss occurs when the body is asleep. 

Limiting water loss in plants 

Terresteral plants have waterproof covering 

Some have restricted supply of water = limiting water loss through transpiration // xerophytes

Modifications of a plant is made by:

- Thick cuticles 

- Rolling up of leaves 

- Hairy leaves 

- Stomata in pits and grooves 

- Reducing surface area to volume ratio of the leaves

Exchange And Transport Systems: - Gas Exchange In Plants

- Gas Exchange in plants - 

Gas exchange is able to occur in plants due to their adaptations.

These adaptations would include - 

Thin = Short diffusion pathway// Carbon dioxide and oxygen can pass in and out of the plant cell. 

Large surface area = this would allow for an effective gas exchange because its able to occur over a larger area. 

Air spaces between the spongy mesophyll = allows a diffusion gradient to be maintained 

Guard cells = controls the amount of Carbon dioxide and oxygen diffuses in and out of the cell. 

For a most gaseous exchange to occur:
- There are many small pores // stomata // no cell is far from a stoma // short diffusion path.
- Numerous interconnecting air-spaces occur throughout the mesophyll
- Large surface area of mesophyll cells // rapid diffusion

Stomata:

Each stoma is surrounded by pair of special guard cells which open and closes the stomata pores // controls the rate of gaseous exchange // plants evolved to balance the conflict between gas exchange and controlling the water loss in the plant.

Exchange And Transport Systems: - Gas Exchange In Fish

- Gas Exchange in fish -

Fish have many different adaptation that give would give the fish large surface area for gas exchange. 

In a fish there are rows of gill filaments which are stacked like pages of a book. 

On the gill filaments there are gill lamellae which has a network of capillaries on them. This provides a larger surface area for gas exchange. 

counter-current flow 

The water enters the mouth of the fish and leaves through the gills. 

As the water passes through the gills the water passes over the filaments and over the lamellae. 

Water and blood flow over and through the lamellae in the opposite direction. // Parallel. 

When the blood first comes close to the water, water is fully saturated with oxygen and the blood has small amounts. 

This creates a steep concentration gradient // oxygen diffuses out of the water and into the blood. 

As the blood is absorbing more oxygen as it moves along the lamellae // blood reaches the end of the lamella 80% saturated with oxygen. The blood is highly saturated than it was at the beginning of the lamellae.

The concentration has continued to be maintained so it can continue to absorb oxygen from the water. 

Concurrent flow 

The water enters the mouth of the fish and leaves through the gills. 

As the water passes through the gills the water passes over the filaments and over the lamellae. 

The blood flows in same direction as the water does.

Water is slightly less saturated as it proceeds to move along the lamellae // water has still highly saturated with oxygen compared to the blood, diffusion still occurs until water and the blood have reached equal saturation. 

The steep concentration gradient continues to decrease as the diffusion of oxygen continues.

Exchange And Transport Systems: - Gas Exchange In Insects

- Gas Exchange in insects -

Insects do not have a transport system so gases would need to transported directly into the respiring tissues. 

Insects use tracheae to exchange gases 

Insects have microscopic air-filled pipes = Tracheae

The air moves into the tracheae through the pores on the surface = Spiracles 

On the insect there are spiracles which are placed along side the body // These spiracles are openings of small tubes running into the insects body. 

Oxygen moves down a concentration gradient towards the cells.

The tracheae branches off into tracheoles //
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Adaptations =
- Thin = quicker rate of diffusion
- Permeable walls = diffusion occurs down a gradient (active transport not needed to pass the molecules)
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Oxygen diffuses into the respiring cells.

Water at the end of the tracheoles allows for a concentration gradient to be maintained // the

Carbon dioxide from the respiring diffuse into the water (higher concentration of CO2 // lower concentration of 02 in the respiring cells).

Rhythmic abdominal movement = moves the air in and out of the spiracles.

Energy Transfer In And Between Organisms: - Link Reaction And Krebs Cycle.

- Link reaction and Kreb cycle - 

Link reaction: 

Pyruvate is oxidised to acetate // pyruvate loses a CO₂ and (X2) H // H is accepted by NAD to reduced NAD later used to produce ATP. 

2-Carbon acetate combines coenzyme A (CoA) = acetylcoenzyme A 

Krebs cycle

2-Carbon acetylcoenzyme A from link reaction combined with the 4-carbon molecule to produce a 6-carbon molecule. 

6-Carbon molecule loses carbon dioxide and hydrogen to give 4-Carbon molecules and single molecule of ATP produced as result of substrate-level phosphorylation 

4-Carbon molecule combines with new molecule of acetylcoenzyme A // cycle starts again. 

Pyruvate, link reaction and krebs cycle produces 

- Reduced coenzymes NAD and FAD // by oxidative phosphorylation potential to provide energy to produce ATP 

- 1 ATP molecule 

- 3 CO₂ molecules

2 Pyruvate molecules produced for each original glucose molecule. 

Coenzymes = molecules that enzymes require to function, includes:

NAD - important throughout repsiration 

FAD - important in the Kreb cycle 

NADP - important in photosynthesis

Respiration NAD important carrier // works with dehydrogenase enzymes catalyse removal hydrogen atoms from substrates transfer them to the other molecules involved in oxidative phosphorylation. 

Kreb cycle is important for: 

Breaking down pyruvate into CO₂ 

Producing hydrogen atoms carried by NAD to electron transfer chain prodivde energy for oxidative phosphorylation = ATP produced 

Regenerates 4 carbon molecule combines with acetylcoenzyme A 

Source of intermediate compounds used by cells - fatty acids, amino acids and chlorophyll. 

Energy Transfer In And Between Organisms: - Glycolysis

- Glycolysis -

2 Different forms of cellular respiration =

Aerobic respiration = requires O₂ produces CO₂, H₂O, ATP 

Anaerobic respiration = takes place absence of O₂ produces lactate or ethanol and CO₂ // little ATP. 

Aerobic respiration summeriesed into 4 stages 

1. Glycolysis 
2. Link reaction 
3. Kreb cycle 
4. Oxidative phosphorylation 

Glycolysis 

1. Phosphorylation of glucose to glucose phosphate = glucose is made reactive with the addition of 2 phosphate molecules (phosphorylation) // Phosphate molecules come from hydrolysis of ATP (X2) ⇒ ADP. // Energy provided to activate glucose lowering activation energy for enzyme controlled reactions 

2. Phosphorylated glucose is split = Glucose is split into 3-carbon triose phosphate (X2) 

3. Triose phosphate is oxidised = H₂ removed from triose phosphate (X2) transformed into hydrogen-carrier molecule NAD to form reduced NAD

4. Production of ATP = enzyme controlled reaction converts triose phosphate into 3-carbon molecule Pyruvate // (X2) molecules of ATP are regenerated from ADP.

From ONE molecule of glucose =

2 ATP molecules // was 4 but 2 was used in initial phosphorylation of glucose - net increase of 2 molecules. 

2 reduced NAD molecules 

2 Pyruvate molecules 

Energy Transfer In And Between Organisms: - Light Independent Reaction

- Light Independent Reaction -

The Calvin Cycle - 

The products of the light dependent reaction is ATP and reduced NADP // both used to reduce glycerate-3-phosphate. 

This would have occur with or without light. 

1. The CO₂ diffuses into the leaf through the stomata // dissolves in water around the walls of mesophyll cells // diffuses through the cytoplasm and chloroplast membrane into the stomata of chloroplast. 

2. In stroma CO₂ reacts with 5 carbon compound   // catalysed by enzyme ribulous bisphosphate carboxylase (Rubisco)

3. Reaction CO₂ + RuBP = 2X 3-carbon glycerate 3-phosphate.

4. Reduced NADP from light dependent reaction, reduces glycerate 3-phosphate ⇒ triose phosphate using energy supplied by ATP. 

5. NADP is re-formed // goes back into the light dependent reaction = gaining protons. 

6. Triose phosphate converted into organic substances // starch, cellulose, lipids, glucose, amino acids, and nucleotides. 

7. Most triose phophate is used to generate ribulose bisphosphate // ATP is used from Light Dependent Reaction . 

Site of the light-independent reaction -

Chloroplast is adapted in carrying out the light independent reaction of photosynthesis. 

The stroma contains a fluid with all the enzymes needed for the light independent reaction. Stromal fluid is membrane-bound in the chloroplast. 

The stroma fluid surrounds the grana // products of light dependent stage in grana can diffuse into stroma 

Contains DNA and ribosomes // can quickly and easily manufacture some of the proteins involved in the light-independent reaction. 

Energy Transfer In And Between Organisms: - Light Dependent Reaction

- Light Dependent Reaction -

Oxidation and Reduction 

Oxidation is when the substance gains oxygen or loses hydrogen. 

Reduction is when the substance loses oxygen or gains hydrogen.

Oxidation results in energy being given out, whearas reduction results in it being taken in. 

Making of a ATP

Photoionisation is a result of the chlorophyll molecule becoming ionised. 

The electrons leave the chlorophyll are taken up by a molecule electron carrier // the chlorophyll is oxidised // electron carrier is reduced. 

Electrons are passed along a series of oxidation-reduction chain reactions. // A transfer chain that is located in membrane of the thylakoids. 

With each carrier the energy level is lowered in the electron, the energy released is used to combine the inorganic phosphate and the ADP molecule to create ATP. 

Chemiosmotic theory

This explains the ATP production 

1.  Proton pumps // protein carrier are used to pump the protons (H+) from the stroma in the thylakoid membrane. 
2. Electrons released from photolysis drives the process as it produces protons // further increase of concentration in the thylakoid space.
3. A concentration gradient is maintained // higher concentration = in the thylakoid space, lower concentration = in the stroma 
4. Protons can only cross the thylakoid membrane through ATP synthesised channel proteins. 
5. The channels for small granules on the membrane surface = stalked granules. 
6. Protons pass through these ATP synthase channels they can cause changes to the structure of the enzyme // catalyse combination of ADP with inorganic phosphate to form ATP. 

Photolysis of water 

2H₂O → 4H+ + 4e⁻  + O² 

Protons are passed out of the thylakoid space through ATP synthase channels taken up by electron carrier = NADP.
On taking up the protons the NADP reduced // the reduced NADP = main product of the light dependent stage and enters the light independent reaction.

Reduced NADP is important because it is further potential source of chemical energy to the plant.
Oxygen is a by-product from the photolysis of water is either used in respiration or diffuses out of the stomata as waste product of photosynthesis.

Site of the light-dependent reaction: 

Chloroplasts are structurally adapted to their functions of capturing sunlight. 

Thylakoid membranes have a large surface area for attachment of chlorophyll, electron carriers and enzymes carry out light-dependent reaction. 

Network of proteins in grana holds the chlorophyll // precise to allows maximum absorption. 

Granal membranes have ATP synthase channels which catalyse the production of ATP // also selectively permeable which allows establishment of proton gradient. 

The chloroplast contain both DNA and ribosomes can quickly and manufacture some of the proteins involved in light-dependent reactions.  

Energy Transfer In And Between Organisms: - Photosynthesis

- Photosynthesis - 

Site of Photosynthesis. 

Within eukaryotic plants this is the main site of photosynthesis // Within the chloroplast of cellular organelles. 

Structure of the leaf.

1. Large surface area = more sunlight is absorbed
2. Arrangement of leaves = avoids overlapping // leaves do not overshadow each other. 
3. Thin // diffusion distance is kept short = light absorbed within few micrometers 
4. Transparent cuticle and epidermis let light through to photosynthetic mesophyll cells 
5. Long, narrow upper mesophyll cells packed with chloroplast = collecting sunlight. 
6. Numerous stomata = gas exchnage // short diffusion pathway from the mesophyll cells 
7. Stomata open and closes = result of light intensity 
8. Many air spaces in lower mesophyll layer to allow rapid diffusion in the gas phase of carbon dioxide and oxygen. 
9. Network of xylem = brings water to leaf cells // Phloem = carries away the sugar (product of photosynthesis) 

There are 3 stages in photosynthesis. 

- Capturing the light energy 

- Light-dependent reaction 

- Light Independent reaction 

Structure of chloroplast and its role.

The grana = 100 discs-like structure = thylakoids // light dependent stage takes place here. 

The stroma = fluid filled matrix // light independent stage occurs here // number of other structures, for example, starch grains.