Biology Topic 8

What is diffusion?

The movement of particles from an area of high concentration to an area of low concentration down a concentration gradient.

What is active transport?

The movement of particles from an area of low concentration to a high concentration, against the concentration gradient using energy.

What is osmosis?

The movement of water molecules from an area of a dilute solution to a more concentrated one through a partially permeable membrane.

What is double circulation?

A circulatory system where blood passes through the heart twice during one complete journey around the body.

What is a red blood cell?

A cell that carries oxygen around the body using haemoglobin.

What is a white blood cell?

A cell in the body that helps defend against pathogens and infection.

What is plasma?

The liquid part of the blood that transports cells and dissolved nutrients around the body.

What are platelets?

Small cell fragments in the blood that help it clot and stop bleeding.

What are coronary vessels?

Blood vessels that supply the heart muscle with oxygenated blood and nutrients.

What is a capillary?

A tiny blood vessel where the exchange of substances takes place.

What is an artery?

A blood vessel that carries blood away from the heart, usually oxygenated.

What is a vein?

A blood vessel that carries blood towards the heart, usually deoxygenated.

What does oxygenated mean?

Blood that is rich in oxygen.

What does deoxygenated mean?

Blood that is low in oxygen and usually high in carbon dioxide.

What is Fick's law?

The rate of diffusion is directly proportional to surface area and concentration difference, and inversely proportional to the thickness of the membrane.

What is oxygen debt?

The extra oxygen needed after exercise to break down lactic acid and restore the body to its resting state.

What is systole?

The phase of the heartbeat when the heart muscle contracts and pumps blood out of the chambers.

What is diastole?

The phase of the heartbeat when the heart muscle relaxes and the chambers fill with blood.

What is aerobic respiration?

The release of energy from glucose using oxygen.

What is cardiac output?

The volume of blood the heart pumps out per minute.

What is anaerobic respiration?

The release of energy from glucose without oxygen.

What is SA:V ratio?

Surface area to volume ratio is the amount of surface area compared to the volume of an object.

Why Diffusion Becomes Insufficient?

As organisms get larger, volume increases faster than surface area

This causes a low surface area to volume ratio

Diffusion distance increases, so diffusion becomes too slow

Diffusion alone cannot supply enough oxygen/nutrients to cells

Folding of Exchange Surfaces

Folding increases the surface area without significantly increasing volume, which increases the surface area to volume ratio and allows more substances to diffuse at a faster rate.

Unicellular organisms

Have a large surface area to volume ratio

Short diffusion distances

Can rely on diffusion alone for exchange

Multicellular organisms

Have a small surface area to volume ratio

Diffusion distances are larger

Diffusion alone is too slow to meet demand

Therefore need specialised exchange surfaces

Alveoli:

large surface area, thin walls, rich blood supply

Villi

: folded surface, thin epithelium, good blood supply

Q: State three factors that affect the rate of diffusion.

A: Surface area, concentration gradient, and diffusion distance.(Temperature may also affect diffusion.)

How does surface area affect diffusion rate?

A: Increasing surface area increases the rate of diffusion because more particles can diffuse at the same time.

Q: How does concentration gradient affect diffusion rate?

A: A shorter diffusion distance increases the rate of diffusion because particles take less time to cross the surface.

Q: Why do unicellular organisms rely entirely on diffusion?

A: They have a large surface area to volume ratio and short diffusion distances, so diffusion is fast enough.

Q: Why do multicellular organisms need specialised exchange surfaces?

A: They have a small surface area to volume ratio and large diffusion distances, so diffusion alone is too slow.

Q: How are alveoli adapted for fast diffusion?

A: Alveoli have a large surface area, thin walls, and a steep concentration gradient, which increases the rate of diffusion.

Q: How do root hair cells increase diffusion rate?

A: Root hair cells have a large surface area and thin cell walls, which increases the rate of diffusion.

Q: How are villi adapted for their function?

A: Villi have a large surface area due to their folded structure, a thin epithelium which reduces diffusion distance, and a good blood supply to maintain a steep concentration gradient, allowing rapid absorption of nutrients.

Q: What is gas exchange in the lungs?

A: Gas exchange is the diffusion of oxygen into the blood and carbon dioxide out of the blood at the alveoli.

Q: Why do alveoli have thin walls?

A: Alveoli have thin walls to reduce diffusion distance, increasing the rate of diffusion.

Q: Why is a moist surface important in alveoli?

A: Moist surfaces allow gases to dissolve, which increases the rate of diffusion.

Q: How does a large surface area of alveoli help gas exchange?

A: A large surface area provides more space for diffusion, increasing the rate of gas exchange.

: Why do alveoli have a dense network of capillaries?

A: Dense capillaries maintain a steep concentration gradient, increasing the rate of diffusion.

Q: How does blood flow help gas exchange in alveoli?

A: Continuous blood flow removes oxygen and brings carbon dioxide, maintaining a steep concentration gradient.

Q: How does ventilation improve diffusion in alveoli?

A: Ventilation keeps oxygen levels high and carbon dioxide levels low, maintaining a steep concentration gradient.

Q: What happens if alveolar walls become thicker?

A: Thicker walls increase diffusion distance, which reduces the rate of diffusion.

Q: What symptom might occur if diffusion is slow and why?

A: Symptoms like dizziness or shortness of breath occur because less oxygen reaches the blood.

Q: How do alveoli maximize the rate of gas exchange?

A: They have a large surface area, thin walls, dense capillaries, and constant ventilation, which together increase diffusion rate.

Q: What is the function of red blood cells?

A: To transport oxygen from the lungs to body tissues.

Q: How are red blood cells adapted to their function?

A:

Biconcave disc shape increases surface area for oxygen diffusion

No nucleus creates more space for haemoglobin

Contain haemoglobin which binds to oxygen

Q: What is haemoglobin?

A: A protein in red blood cells that binds with oxygen to form oxyhaemoglobin.

Q: What is the function of white blood cells?

A: To defend the body against pathogens.

Q: Name two ways white blood cells fight infection.

A:

Produce antibodies

Engulf pathogens by phagocytosis

Q: What is the function of platelets?

A: To help blood clot and prevent blood loss.

Q: How do platelets prevent blood loss?

A: They trigger clotting by forming fibrin from fibrinogen, which creates a mesh that seals the wound.

Q: What is plasma and what does it transport?

A: Plasma is a yellow straw-coloured liquid that transports blood cells, nutrients, hormones, carbon dioxide, urea and platelets.

Q: Why do arteries have thick muscular walls?

A: Because blood flows through arteries at high pressure, so thick walls prevent them from bursting.

Q: Why do veins have valves?

A: To prevent backflow of blood, especially because blood pressure is low.

Q: Why do veins have a large lumen?

A: To reduce friction and allow blood to flow easily at low pressure.

Q: How are capillaries adapted for exchange? (3 marks)

A:

Walls are one cell thick, reducing diffusion distance

Very narrow lumen slows blood flow

Allows efficient diffusion of oxygen, carbon dioxide, nutrients and waste

Q: What is double circulation?

A: Blood passes through the heart twice in one complete circuit of the body.

Q: Why is double circulation important?

A: It maintains high pressure to the body and low pressure to the lungs, making oxygen delivery more efficient.

Q: What is cardiac output?

A: The volume of blood pumped by the heart per minute.

Q: State the equation for cardiac output.

A:Cardiac output = heart rate × stroke volume

Q: Define respiration.

A: Respiration is an exothermic reaction that releases energy from glucose.

Q: Word equation for aerobic respiration?

Glucose + oxygen → carbon dioxide + water (+ energy)

Q: Word equation for anaerobic respiration in muscles?

A:Glucose → lactic acid (+ energy)

Q: Why does anaerobic respiration release less energy?

A: Because glucose is not fully broken down without oxygen.

Q: What is oxygen debt?

A: The extra oxygen needed after exercise to break down lactic acid.

Q: What does a respirometer measure?

A: The rate of respiration by measuring oxygen uptake.

Q: Why is soda lime used in a respirometer?

A: To absorb carbon dioxide so changes in gas volume are due only to oxygen upta

Q: How does temperature affect respiration rate?

A: As temperature increases, respiration rate increases because enzymes work faster (up to the optimum).

Q: Why do active organisms respire faster than inactive ones?

A: They require more energy for movement, so they use more glucose and oxygen.