StemUp: OCR A A level Biology 3.1.1 Exchange surfaces

How do single-celled organisms exchange substances with their environment? (2)

- Single celled organisms have a large SA:V

- Allowing substances to enter easily and quickly by simple diffusion due to the short diffusion distance

Why do multicellular organisms need specialised exchange surfaces? (3)

- They have a small surface area to volume ratio, making diffusion less efficient

- Some cells are deep within the body, increasing diffusion distance

- Multicellular organisms have a higher metabolic rate than single-celled organisms

How do you calculate the surface area to volume ratio? (2)

- Divide the surface area

- By the volume

Why are specialised transport systems needed in multicellular organisms? (2)

- They ensure that dissolved gases and other substances

- Can move to and from respiring tissues quickly and efficiently

How do small terrestrial animals like worms exchange gases? (4)

- Worms use their moist outer body surface for gas exchange

- They have an elongated body to increase SA:V ratio

- They also have a primitive circulatory system

- To maintain a concentration gradient for efficient gas exchange

How does a large surface area aid with exchange in root hair cells? (2)

- Increases the rate of water absorption by osmosis and mineral ion uptake

- By active transport from the soil

Why is a thin exchange surface in the alveoli important for diffusion? (3)

- Made of a single layer of thin, flat cells called alveolar epithelium

- This decreases the diffusion distance for oxygen (O₂) and carbon dioxide (CO₂)

- Increasing the rate of diffusion

How do alveoli maintain a concentration gradient for efficient gas exchange? (4)

- Alveoli are surrounded by a capillary network

- Providing a constant blood supply to carry O₂ away and bring CO₂ to the alveoli.

- The lungs are also ventilated, replacing air in each alveolus

- To maintain a concentration gradient of O₂ and CO₂

What are the fish gills? (2)

- The gas exchange surface in fish

- Exchanging O₂ and CO₂ between the blood and surrounding water

How do fish gills facilitate efficient gas exchange? (3)

- They have a network of capillaries for a good blood supply and are well ventilated as fresh water passes over them

- These features maintain a concentration gradient for O₂

- Increasing the rate at which O₂ diffuses into the blood

What are the key features of the lungs as a gas exchange surface in mammals? (4)

- Large surface area due to many alveoli

- Short diffusion distance between alveoli and blood

- Alveoli have a thin fluid layer to dissolve respiratory gases

- Highly developed circulatory system.

What is the pathway of air through the mammalian gaseous exchange system? (2)

- Air enters through the trachea, which splits into bronchi, each leading to a lung

- The bronchi branch into bronchioles, which end in alveoli (site of gas exchange)

What is the role of goblet cells in the gaseous exchange system? (2)

- Secrete mucus to trap bacteria and dust

- Reducing the risk of infection

What is the role of ciliated epithelium in the gaseous exchange system? (2)

- Moves mucus towards the throat

- Preventing lung infections

What is the function of elastic fibres in the lungs? (2)

- Stretch during inhalation and recoil during exhalation

- Controlling airflow

What is the role of smooth muscle in the lungs? (2)

- Controls the diameter of airways by contracting or relaxing

- Making airflow easier during exercise

What is the function of cartilage rings in the trachea and bronchi? (2)

- Support the trachea and bronchi

- Preventing collapse during breathing

What happens during inspiration in mammals? (4)

1. External intercostal muscles and diaphragm contract

2. Causing the ribcage to move up and out

3. Increasing the thorax volume and decreasing lung pressure

4. Air flows into the lungs (inspiration is an active process)

What happens during expiration in mammals? (4)

1. External intercostal muscles and diaphragm relax

2. Ribcage moves down and in

3. Decreasing thorax volume and increasing lung pressure

4. Air is forced out of the lungs (normal expiration is a passive process)

What happens during forced expiration? (2)

- The internal intercostal muscles contract

- Forcing air out (this process is not passive)

What is tidal volume? (1)

The volume of air taken in with each breath

What is vital capacity? (1)

The maximum volume of air that can be breathed in or out

What is breathing rate? (1)

The number of breaths taken per minute

What is oxygen consumption/uptake? (1)

The rate at which an organism uses up oxygen

What is a spirometer? (2)

- Device used to investigate breathing

- By measuring the movement of an oxygen-filled chamber with a movable lid

How does a spirometer work? (2)

1. As the person breathes in and out, the lid moves up and down

2. The movements are recorded to create a spirometry trace

Draw and label a graph produced by spirometer

Why does the total volume of gas in the spirometer chamber decrease over time? (4)

- Exhaled air contains carbon dioxide

- Which is absorbed by soda lime

- Leaving only oxygen in the chamber

- As the oxygen is used for respiration, the total volume decreases

Why do bony fish need a specialised gas exchange surface (gills)? (2)

- They are multicellular, with a small surface area to volume and impermeable skin

- So they need gills for gas exchange

How do gills provide a large surface area for gas exchange? (2)

- Have thin branches called gill filaments/primary lamellae and gill plates/secondary lamellae

- Which further increase their SA

What is the counter-current system in fish gills? (4)

- Blood flows through gill plates in one direction

- Water flows in the opposite direction

- Maintaining a large concentration gradient between the water and blood

- The concentration of oxygen in the water is always higher than in the blood, maximizing oxygen diffusion into the blood

How do fish ventilate their gills? (5)

1. Fish opens its mouth

2. Lowering the floor of the buccal cavity

3. Increasing the volume and decreasing pressure, which sucks water in

4. When the fish closes its mouth, the floor of the buccal cavity is raised

5. Decreasing volume and increasing pressure, which forces water over the gill filaments

What is the operculum, and what is its function? (1)

Bony flap that covers and protects the gills in fish

Why do insects need a specialised gas exchange surface? (2)

- They have a hard exoskeleton unsuitable for gas exchange

- So they require a tracheal system to transport oxygen directly to respiring cells

How does the tracheal system in insects work? (3)

1. Air enters through spiracles (pores on the insect's surface)

2. Oxygen travels down its concentration gradient through tracheae and tracheoles, which have thin, permeable walls and lead to individual cells

3. Oxygen dissolves in the fluid inside the tracheoles and diffuses into cells, while carbon dioxide moves in the opposite direction

How do insects ventilate their tracheal system? (3)

1. Rhythmic abdominal movements change the volume of their bodies

2. Moving air in and out of the spiracles

3. Larger insects use wing movements to pump their thoraxes

How do you dissect the gaseous exchange system of a bony fish? (3)

1. Place the fish on a dissection tray

2. Push back the operculum and use scissors to remove the gills

3. Cut each gill arch through the bone at the top and bottom to see the gill filaments

How do you dissect the gaseous exchange system of an insect? (4)

1. Fix the insect (e.g., grasshopper or cockroach) to a dissection board using dissecting pins

2. Cut and remove a piece of the exoskeleton from the abdomen

3. Fill the abdomen with saline solution using a syringe to reveal tracheae, which appear as silver-grey tubes filled with air

4. Examine the tracheae under a microscope using a wet mount slide

What structures can be seen in the insect trachea under a microscope? (2)

- Rings of chitin in the walls of the tracheae

- Which function to support the tracheal tubes