Biology - Chapter 6: Exchange

2 types of exchange

1. Passive: uses no metabolic energy (only kinetic energy of particles) - diffusion and osmosis
2. Active: uses metabolic energy - active transport

What is the relationship between diffusion, surface area, difference in concentration and length of diffusion path?

diffusion is proportional to (SA x difference in conc)/length of diffusion path

In insects, what is a problem that arises when they increase in surface area?

More water is lost as water evaporates from them

3 ways respiratory gases move in and out of the tracheal system in insects

1. Along a diffusion gradient
2. Mass transport
3. Tracheole ends fill with water

Why are respiratory gases exchanged along a diffusion gradient in air rather than in water?

Diffusion in air is much more rapid than in water.

What is the countercurrent flow and how does it work?

Blood and water flow in opposite directions so blood always passes water with a higher oxygen concentration.
This means that diffusion gradient is maintained along the length of the lamella so diffusion occurs along the length of the lamella.

In plants, what happens when photosynthesis is not occuring?

Oxygen diffuses into the leaf as it is being constantly used by the cells in respiration, while CO2 diffuses out as it is produced.

6 features of xerophytes that reduce the rate of water loss via evaporation

1. Thick cuticle layer: increases diffusion distance so reduced water loss
2. Rolling up of leaves: traps water vapour, reduces water potential gradient so reduced water loss
3. Hairs: traps water vapour, reduces water potential gradient so reduced water loss
4. Sunken stomata (i.e. in pits/grooves): traps water vapour, reduces water potential gradient so reduced water loss
5. Spines/needles: reduces SA:V ratio,
6. Waxy cuticle layer: reduces evaporation/transpiration

4 parts of the gross structure of the human gas exchange system

1. Trachea
2. Bronchi
3. Bronchioles
4. Alveoli

2 features of the bronchi

1. Larger bronchi supported by cartilage (smaller ones not) - prevent collapse
2. Have goblet cells to secrete mucus and cilia to waft it towards the throat

Other words for inhalation and exhalation

Inspiration and expiration

Is inspiration an active or passive process?

Active - uses energy

Is expiration an active or passive process?

Passive - doesn't require much energy

Another name for capillary endothelium is....?

Squamous epithelium

Risk factor

Something that increases the chance of getting a disease

In the digestive system, what is the function of enzymes?

To hydrolyse large molecules into smaller ones that can be absorbed into the bloodstream

7 main parts of the digestive system and their function

1. Oesophagus: carries food from mouth to stomach
2. Stomach: stores and digests food (especially proteins) - secretes enzymes
3. Small intestine (ileum): food is further digested, secretes enzymes to do so
4. Large intestine: absorbs water
5. Rectum: stores faeces before it is removed by the anus (ejection)
6. Salivary glands: secretes enzymes, including amylase
7. Pancreas: a large gland that produces 'pancreatic juice' - contains proteases, lipase and amylase

3 types of digestive enzymes and what they hydrolyse

1. Carbohydrases: carbohydrates -> monosaccharides
2. Lipases: lipids -> fatty acids and glycerol
3. Proteases: proteins -> amino acids

Where is amylase produced?

The salivary glands and the pancreas

Name 4 membrane-bound enzymes and what they hydrolyse

1. Maltase: maltose -> glucose
2. Sucrase: sucrose -> glucose + fructose
3. Lactase: lactose -> glucose + galactose
4. Dipeptidases: dipeptide -> amino acids

What is a monoglyceride?

One glycerol and one fatty acid

Name 3 peptidases and explain their function

1. Endopeptidases: hydrolyse peptide bonds in the middle of a polypeptide, forms shorter polypeptides
2. Exopeptidases: hydrolyse peptide bonds at the end of polypeptides, removing terminal amino acids and forming dipeptides
3. Dipeptidases: hydrolyses peptide bond between two amino acids in a dipeptide to form single amino acids

Give 3 functions of bile salts

1. Emulsify lipids and fats
2. Increase surface area of lipids to increase lipase activity
3. Form micelles

Why is the rate of digestion faster with both endopeptidases and exopeptidases, when compared to only using exopeptidases?

Endopeptidases create more ends, increasing the surface area for exopeptidases to act on

Tissue fluid

The environment around the cells of multicellular organisms

Why can't multicellular organisms rely on diffusion?

The majority of cells are too far from exchange surfaces

Mass transport system

a transport system where substances are transported in a mass of fluid to maintain the diffusion gradient that brings materials to and from the cell-surface membranes.

2 factors that affect the amount of each material that is exchanged in an organism

Size and metabolic rate

4 examples of things that need to be interchanged between an organism and its environment

1. Respiratory gases (oxygen, carbon dioxide)
2. Nutrients (glucose, fatty acids, amino acids, vitamins, minerals)
3. Excretory products (urea, carbon dioxide)
4. Heat

What happens when an organism's size increases?

Its volume increases at a faster rate than their surface area - they have a smaller surface area to volume ratio

Why does having a smaller SA:V ratio reduce the rate of diffusion?

It would take too long for the substances to reach the middle of the organism

5 features of specialised exchange surfaces

- Large SA relative to volume: increases SA:V ratio to increase rate of diffusion
- Very thin: short diffusion pathway to increase rate of diffusion
- Selectively permeable: allow selected materials to cross
- Movement of the environmental medium: maintain steep concentration gradient (e.g. the air)
- A transport system: ensure the movement of the internal medium to maintain a steep concentration gradient (e.g. the blood)

Why are specialised exchange surfaces often located inside an organism?

They are thin, so are easily damaged and dehydrated.

2 features of gas exchange in single-celled organisms

- Small, so have large SA:V ratio
- Short diffusion pathway - only one cell

Tracheae and give an adaptation

- Internal network of tubes in insects
- Supported by strengthened rings to prevent tracheae from collapsing
- Tracheoles: smaller dead-end tubes the trachea divide into that extend throughout all the body tissues of the insect so atmospheric air is brought directly to respiring tissues (short diffusion pathway)

How does gas exchange in insects occur along a diffusion gradient?

- Cells respire, oxygen used up so conc at end of tracheoles falls - this causes gradient so more oxygen diffuses.
- CO2 produced during respiration creates gradient in opposite direction.

How does gas exchange in insects occur via mass transport?

Contraction of insect muscles in abdomen results in more air/oxygen entering + it enters faster, maintaining a greater diffusion gradient

How does gas exchange in insects occur when the ends of tracheoles are filled with water?

- During periods of major activity, muscle cells around tracheoles respire anaerobically, producing lactate - soluble, lowers water potential of muscle cells.
- Water moves into tracheole cells by osmosis
- Water in tracheole ends decrease in volume, drawing air further into them
- Final diffusion pathway is in a gas phase rather than liquid phase so diffusion is more rapid
- Increases the rate of diffusion but leads to greater water evaporation

How do gases enter and leave tracheae?

- Enter via tiny pores on the body surface called spiracles
- Spiracles may be opened/closed by a valve
- Water vapour can evaporate when spiracles are open so insects keep them closed to reduce water loss
- Open spiracles to allow gas exchange

What is a limitation of the tracheal system in insects?

- Relies mostly on diffusion to be effective - needs short diffusion pathway (insects must be small)
- Length of diffusion pathway is limited by the size the insects can attain

4 features of gills (fish)

1. Many gill lamellae/filaments: increase surface area of the gills (at a right angle to the filaments)

2. Thin - short diffusion pathway

3. Countercurrent flow (water flows over gill lamellae is in opposite direction to the flow of blood) - diffusion gradient maintained, so diffusion takes place along whole length of lamellae

4. Many capillaries - maintains steep concentration gradient

What would happen if there was no countercurrent flow in fish gills?

Water and blood would flow in the same direction - diffusion gradient would only be maintained across a part of the gill lamellae so lower proportion of oxygen from the water would be absorbed into the blood

4 insect adaptations to reduce water loss

1. Exoskeleton made of chitin with lipid layer - protection + waterproof to reduce water loss
2. Spiracles can close to reduce water loss (normally closed when at rest as need to be open to take in oxygen)
3. Hairs around spiracles - traps layer of air saturated with water to reduce water loss
4. Small surface area to volume ratio so smaller area where water can evaporate from

2 ways gas exchange in plants is similar to gas exchange in insects

1. No living cell is far from the external air (short diffusion pathway)
2. Diffusion takes place in the gas phase (more rapid than if in water)

3 adaptations of leaves for a faster rate of diffusion

1. Many stomata - no cell is ever far from stomata so short diffusion pathway
2. Many air spaces in the spongy mesophyll - larger surface area of cells can come in contact with air so more diffusion
3. Large surface area of mesophyll cells - rapid diffusion

How does the stomata work? (5)

- Stomata surrounded by guard cells
- When there's a lot of water, water enters guard cells by osmosis
- Guard cells swell, become turgid -> stomata open
- Guard cells shrink and stomata close when not a lot of water, less photosynthesis
- This enables gas exchange and reduces the rate of water loss (by evaporation or diffusion)

2 terrestrial plant adaptations to reduce water loss

1. Waxy upper cuticle - waterproof, prevents loss of water via evaporation
2. Stomata on underside of leaves that can close - stay closed when little photosynthesis to reduce loss of water

Xerophytes

Plants that are adapted to living in dry conditions in areas where water is in short supply

2 other adaptations of xerophytes (not linked to reducing water loss)

1. Widespread, shallow roots: absorbs water quickly from surface level of ground after rain
2. Long, deep tap roots: absorb groundwater / water deep underground

Why do mammals need to absorb a large volume of oxygen and remove a large volume of carbon dioxide?

1. They're relatively large organisms with a large number of cells
2. They maintain a high temperature, high metabolic rates and high respiratory rates

Why are lungs located inside the body?

- Air is not dense enough to support and protect them (delicate)
- Body would lose a lot of water and dry out

2 features of the trachea

1. Supported by rings of cartilage: prevents trachea from collapsing due to change of pressure within thorax
2. Tracheal walls made of muscle: have ciliated epithelium and goblet cells - goblet cells secrete mucus and cilia waft it towards the throat to destroy pathogens

1 feature of the bronchioles

Made of muscle lined with epithelial cells: muscles allow it to constrict, can control flow of air in and out of alveoli

Ventilation

The movement of air into and out of the lungs

What happens during inspiration?

1. External intercostal muscles contract, internal intercostal muscles relax
2. So the ribcage is pulled up and out
3. Diaphragm muscles contract, flatten and move down
4. These all increase volume of the thorax
5. Increasing thorax volume decreases the pressure in the lungs
6. Air moves from higher pressure in the atmosphere to lower pressure in the lungs (down pressure gradient) - air is forced into the lungs

What happens during expiration?

1. Internal intercostal muscles contract, external intercostal muscles relax
2. So the ribcage is pulled down and in
3. Diaphragm muscles relax, curve and move up
4. These all decrease volume of the thorax
5. Decreasing thorax volume increases the pressure in the lungs
6. Air moves from higher pressure in the lungs to lower pressure in the atmosphere (down pressure gradient) - air is forced out of the lungs

6 features of alveoli that increase the rate of gas exchange

1. Red blood cells are slowed as they pass through pulmonary capillaries: more time for diffusion
2. RBC are flattened against capillary walls: reduces distance between alveolar air and RBC (shorter diffusion pathway)
3. Walls of alveoli and capillaries are thin - 1 cell thick: short diffusion pathway
4. Alveoli and pulmonary capillaries have a very large total SA: increased SA:V
5. Breathing: constantly ventilates lungs + maintains steep concentration gradient
6. Circulation of blood around the body, pumped by the heart: maintains steep concentration gradient

Correlation

When a change in one variable is reflected by a change in the other variable

Why is data showing a correlation between a risk factor and an event not enough to conclude that the factor causes the event?

Correlation does not mean that there is a causal link - there should be a causal relationship with experimental evidence to prove it

5 risk factors of COPD

1. Smoking
2. Air pollution
3. Genetics
4. Infections
5. Occupation

How does oxygen in the air in the alveoli enter the blood in capillaries?

Diffuses across the alveoli epithelium and capillary endothelium

How is the ileum adapted for absorption? (8)

1. Villi and microvilli increase SA for diffusion
2. Have lots of mitochondria: carry out aerobic respiration to be used in active transport
3. Carrier proteins for active transport
4. Carrier proteins and channel proteins for facilitated diffusion
5. Co-transport protein for co-transport of Na+ and glucose/amino acids
6. Very thin: shorter diffusion pathway
7. Have muscles: can contract, mixing ileum contents to maintain steep concentration gradient
8. Well supplied with blood vessels: transport absorbed molecules away, maintain steep concentration gradient

2 stages of digestion

1. Physical digestion: food is ground down into smaller pieces (e.g. by teeth or with muscles in the stomach) so it is easier to ingest + has a larger SA to increase rate of chemical digestion
2. Chemical digestion: digestive enzymes hydrolyse large insoluble molecules into smaller, soluble ones

Describe how starch is hydrolysed (5)

1. Saliva is secreted by salivary glands - has mineral salts which keeps pH neutral (amylase's optimum)
2. It contains amylase, which hydrolyses starch into maltose by breaking glycosidic bonds of starch molecule
3. Food travels down oesophagus to stomach - HCl is acidic so causes amylase enzymes to denature, stopping further starch hydrolysis
4. Food enters small intestine - pancreas secretes pancreatic juice, which contains pancreatic amylase to hydrolyse any remaining starch into maltose; also contains pancreatic salts to keep pH around neutral
5. Maltase is part of CSM of epithelial cells that line ileum and hydrolyses the maltose into a-glucose

Membrane-bound disaccharidase

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 - they hydrolyse disaccharides into monosaccharides

Describe how lipids are digested (3)

1. Bile salt produced by liver: emulsify fat globules to form micelles, increases SA + neutralises HCl from stomach (optimum alkaline conditions)
2. Lipases secreted by pancreas, hydrolyse ester bond between glycerol and fatty acids
3. Forms fatty acids and monoglycerides

Where are lipases produced?

The pancreas

Lumen

The hollow cavity inside a tubular structure

How are amino acids and monosaccharides absorbed into the blood in the ileum?

Co-transport

Exocytosis

The outward bulk transport of materials through the cell-surface membrane.

How does CO2 enter the stomata? (4)

- CO2 enters via stomata
- Stomata opened by guard cells
- CO2 diffuses through air spaces
- Down diffusion/concentration gradient

How does an asthma attack result in a decrease in forced expiration volume? (4)

- Muscle walls of bronchi/bronchioles contracts
- Walls of bronchi/bronchioles secrete more mucus
- Diameter of airways reduced
- So flow of air reduced

Why do smaller organisms have a greater metabolic rate? (3)

They have a greater surface area to volume ratio, so experience greater/faster heat loss - they also have a faster rate of respiration, which releases heat

How are triglycerides absorbed into the blood? (6)

1. Micelles contain bile salts, fatty acids and monoglycerides
2. Micelles make FA/MG more soluble in water and bring them to the lining of the epithelium
3. The monoglycerides and fatty acids are absorbed by diffusion into the epithelial cell (as they are small and non-polar)
4. They are transported to the smooth endoplasmic reticulum, where they are recombined to form triglycerides.
5. Then, in the Golgi apparatus, they associate with cholesterol and lipoproteins to form chylomicrons
6. Chylomicrons move to cell membranes by exocytosis into lymphatic capillaries called lacteals

Describe the role of micelles in the absorption of fats into the cells lining the ileum (5)

1. Micelles include bile salts and fatty acids
2. They carry fatty acids to the lining of the epithelium
3. They make fatty acids more soluble in water
4. They maintain a higher concentration of fatty acids to the lining of the ileum
5. The fatty acids are then absorbed by diffusion into the cells lining the ileum

Describe the role of the Golgi apparatus in the absorption of fats into the cells lining the ileum (2)

1. It modifies triglycerides by combining them with cholesterol and lipoproteins to form chylomicrons
2. It forms vesicles and packages the chylomicrons for exocytosis

5 insect adaptations for efficient diffusion

1. Tracheole walls are thin - short diffusion pathway
2. Tracheoles are highly branched - short diffusion pathway
3. Tracheoles are highly branched - large surface area
4. Tracheae provide tubes full of air - fast diffusion into tissues
5. Fluids at ends of tracheoles that moves out into tissues during exercise - faster diffusion through air to gas exchange surface
6. Body can be moved by muscles to move air - maintains diffusion gradient for oxygen and CO2

What happens to the length of the diffusion pathway as surface area to volume ratio decreases?

The diffusion pathway becomes longer - it takes longer for substances to diffuse