PRAY8 Review Quiz

Approximately how many times more red blood cells are there than white blood cells in human blood?

• About 20 times
• About 200 times
• About 1000 times
• About 2000 times

Answer explanation

According to the text, an adult has at least 20 trillion red blood cells, with about 5 million per cm³ of blood, compared to far fewer white blood cells - approximately 700 times more red blood cells.

What is the main function of haemoglobin in red blood cells?

• To fight infection
• To help blood clot
• To transport oxygen
• To produce energy

Answer explanation

Haemoglobin is a red pigment that carries oxygen. It combines with oxygen to form oxyhaemoglobin.

Why don't red blood cells have mitochondria?

• To make them smaller
• To prevent them using oxygen themselves
• To make them move faster
• To store more haemoglobin

Answer explanation

Scientists think that not having mitochondria stops red blood cells from using up all the oxygen for themselves, instead of delivering it elsewhere.

Which of these is transported dissolved in blood plasma?

• Red blood cells
• Oxygen only
• Glucose
• Haemoglobin

Answer explanation

Glucose is dissolved in blood plasma and transported from the digestive system to every cell in the body.

Carbon dioxide produced in respiring cells is transported to the lungs by:

• Red blood cells only
• Dissolved in plasma only
• White blood cells
• Both dissolved in plasma and in red blood cells

Answer explanation

Carbon dioxide dissolves in blood plasma and is carried away from cells. The blood takes it to the lungs where it diffuses out.

Which statement about alveoli is correct?

• They have thick walls
• They have a small surface area
• They are surrounded by capillaries
• They contain no oxygen

Answer explanation

As blood flows through tiny capillaries next to the alveoli in the lungs, oxygen from the air diffuses into the blood through thin walls.

Why are the walls of alveoli very thin?

• To make breathing easier
• To allow quick diffusion of gases
• To store more air
• To protect the lungs

Answer explanation

There are only two very thin cells between the air and the blood in the alveoli, which allows for efficient gas exchange by diffusion.

Oxygen diffuses from the alveoli into the blood because:

• The blood has more oxygen
• There is a concentration gradient
• The air has less oxygen
• Blood pulls oxygen in

Answer explanation

Oxygen moves from where there is a lot (in the air) to where there are fewer (in the blood) - this is diffusion down a concentration gradient.

What is gas exchange?

• Breathing in and out
• Oxygen entering and carbon dioxide leaving the blood
• Mixing of different gases
• Converting oxygen to carbon dioxide

Answer explanation

Gas exchange is when oxygen from the air goes into the blood and carbon dioxide from the blood goes into the air.

Where does aerobic respiration happen in cells?

• In the nucleus
• In the cell membrane
• In the mitochondria
• In the cytoplasm only

Answer explanation

Mitochondria carry out aerobic respiration, releasing energy from glucose so cells can use it.