B2. Cells

Question 1

What are cells?

Answer 1

The small building blocks that make up all living organisms.

Question 2

State the functions of the ‘cell membrane’

Answer 2

• Forms a barrier between the cell and its surrounding
• Keeps contents to cell inside
• Allows simple substances to enter and leave the cells, e.g. oxygen, carbon dioxide and water
• Controls movement of other substances into and out of the cell, e.g. glucose
• Often described as partially permeable

Question 3

State the functions of the ‘nucleus’

Answer 3

• Controls all activities in the cell

- Controls how cells develop

Question 4

State the functions of the ‘cytoplasm’

Answer 4

• Place where many chemical reactions take place, e.g. respiration and making proteins for the cell

Question 5

State the functions of the ‘chloroplast’

Answer 5

• Photosynthesis

- Stores starch

Question 6

State the functions of the ‘cell wall’

Answer 6

• Stops cells from bursting when they fill with water
• Gives shape to cells
• Allows water and dissolved substances to pass through freely (often described as freely or fully permeable)

Question 7

State the functions of the the ‘vacuole’

Answer 7

• Full of water to maintain shape and ‘firmness’ of cell

- Stores salts and sugars

Question 8

How to calculate the magnification?

Answer 8

Image size / Actual size

Question 9

Describe the structure of an animal cell

Answer 9

• Contains a cell membrane, nucleus, cytoplasm, mitochondrion

Question 10

Describe the structure of a plant cell (palisade)

Answer 10

• Contains a cell wall, cell membrane, vacuole, cytoplasm, nucleus, chloroplasts`

Question 11

Adaptations of root hair cells to its function

Answer 11

• Long extensions that give them a large surface area to absorb water from the soil.
• Thin cell walls - shorter distance for diffusion

Question 12

Adaptations of ciliated cells to its function

Answer 12

• Found in air passages in the lungs (trachea and bronchi)
• Beat back and forth to create a current in the fluid next to the cell surfaces.
• Move mucus that traps dust and pathogens up to the nose and throat.

Question 13

Adaptations of red blood cells to its function

Answer 13

• Contain protein haemoglobin that carries oxygen.

- Biconcave shape - provides large SA compared with their volume which makes it efficient to absorb oxygen.

Question 14

Describe the levels of organisation

Answer 14

Cells -> tissue -> organs -> organ system

Question 15

Define ‘diffusion’

Answer 15

The net movement of molecules from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of their random movement.

Question 16

Name the factors that affect diffusion

Answer 16

• Distance (the shorter the better) e.g. thin walls of alveoli and the capillaries.
• Concentration gradient (the bigger the better). This can be maintained by removing the substance as it passes across the diffusion surface.
• Size of the molecules (the smaller the better).
• Surface area for diffusion (the larger the better) e.g. there is millions of alveoli in a lung, giving a huge surface area for diffusion of oxygen.
• Temperature (molecules have more kinetic energy at higher temperatures).

Question 17

Describe the importance of diffusion of gases and solutes and of water as a solvent

Answer 17

• Oxygen: from alveoli -> blood capillaries
• Carbon dioxide: from blood capillaries -> alveoli; from air -> stomata into leaf for photosynthesis
• Soluble food products from digestion: from small intestine -> blood capillaries
• Scent made of tiny molecules: flowers -> bee’s body

Question 18

Define ‘osmosis’

Answer 18

The diffusion of water molecules from a region of their higher concentration (dilute solution) to region of their lower concentration (concentrated solution), through a partially permeable membrane.

Question 19

Describe the importance of osmosis in the uptake of water in plants

Answer 19

• Usually, the water in the soil is more dilute than that in root hair cells
• So water enters root hair cells by osmosis (a passive process – requiring no energy)

Question 20

Describe the effects of osmosis on plant and animal cells

Answer 20

• When placed in pure water, plant and animal cells will take in the water by osmosis;
• This is because there is a higher concentration of water molecules outside the cell than inside it;
• Plants become turgid, but do not burst because of their tough cell wall;
• Animal cells will burst, because they have no cell wall;
• The reverse happens when plant and animal cells are placed in a concentrated sugar or salt solutions. This is because there is a higher concentration of water molecules inside the cell than outside it;
• Plant cells become flaccid and the cytoplasm is no longer pressed against the cell wall;
• Animal cells also become flaccid and their shape changes- they can become crenated.

Question 21

Describe and explain the importance of a water potential gradient in the uptake of water by plants.

Answer 21

• Water potential is the correct term for saying ”water concentration” a high water potential is equivalent to a low solute concentration and vice versa;
• For plants to take in water through their roots they must have a high solute concentration or low water potential in the roots and low solute concentration or high water potential outside the roots.
• In osmosis, water molecules diffuse down a water potential gradient.