2 Cells

Question 1

Structure of a typical plant cell

Answer 1

Cell membrane, cytoplasm, nucleus, mitochondria, cell wall, large vacuole and chloroplasts.

Question 2

Structure of a typical animal cell
(also what plant and animal cells have in common)

Answer 2

Cell membrane, cytoplasm, nucleus, mitochondria.

Question 3

Function of Cell membrane

Answer 3

Holds cell together and controls substances entering and leaving the cell.

Question 4

Function of Cytoplasm

Answer 4

Supports many small cell structures and is where many different chemical processes happen, contains enzymes that speed up these reactions. Contains water and many solutes are dissolved in it.

Question 5

Function of Nucleus

Answer 5

Contains genetic material in the chromosomes. These control how a cell grows and works. Nucleus also controls cell division.

Question 6

Function of (plant) Cell wall.

Answer 6

Made of cellulose, gives extra support and defines its shape. Provides a semi-permeable surface for molecules to pass in and out of the cell.

Question 7

Function of (plant) Vacuole

Answer 7

Contains cell sap. Used for storage of some materials, support shape of cell. If not enough cell sap in vacuole, plant may wilt.

Question 8

Function of Chloroplasts

Answer 8

Contain the green pigment chlorophyll which absorbs the light energy that plants need to make food in the process known as photosynthesis.

Question 9

Examples of specialised cells

Answer 9

Ciliated cells, red blood cells, sperm cells, egg cells in humans.
Root hair cells and palisade mesophyll cells in plants.

Question 10

Structure and function of Ciliated cells

Answer 10

Cilia: tiny hair-like projections that cover the surface of certain types of cells. Can move and cell can coordinate movement to make waves that pass over the cell. Waves used to move mucus in trachea and bronchi. Tiny particles of dust or bacteria trapped in the mucus are carried along the flow. and pass up the tubes. They are then emptied into the oesophagus and swallowed into the stomach. This keeps lungs clean.

Question 11

Structure and function of palisade mesophyll cells

Answer 11

Plant cells found in upper part of leaf. Most photosynthesis happens here.

Question 12

Structure and function of red blood cells

Answer 12

They do not have a nucleus so cannot divide. Filled with haemoglobin which can pick up oxygen in the lungs and release it near the cells that need it deep inside the body. Biconcave shape so innermost part of red blood cell is never far away from outside, so diffusion in and out happens rapidly. Made in bone marrow and lasts 120 days before being destroyed in the spleen and liver.

Question 13

Function and structure of human sperm cell

Answer 13

Relatively small compared to egg cell. Small vesicle of enzymes called acrosome at the tip of the cell. Enzymes of acrosome digest a hole in the egg cell membrane to allow nucleus of sperm cell to enter egg cell and fuse with its nucleus. Midpiece of sperm cell contains many mitochondria to provide energy to move the flagellum which powers the cell to move.

Question 14

Function and structure of a human egg cell

Answer 14

Very large cell and almost visible without microscope. Cannot move on its own. Large amount of cytoplasm around nucleus provides nutrients for when the cell is fertilised and starts to divide.

Question 15

Function and structure of root hair cells

Answer 15

Water and (dissolved) minerals absorbed by root hairs, very fine extensions of root hair cells on root surface, just behind growing tip of a root. Elongated shape increases surface area available for absorption. As they age, they develop waterproof layers and become non-functional.

Question 16

Define diffusion

Answer 16

the net movement of particles 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 17

Diffusion in cells and Examples

Answer 17

Particles that are small enough can move through cell membranes. These membranes are said to be partially permeable. Diffusion may happen more in one direction than the other depending on concentration.

Blood vessels in the lungs: oxygen from alveoli into red blood cells.
Carbon dioxide entering leaf cells.
Digested food substances from small intestine entering blood.

Question 18

Define osmosis

Answer 18

the net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane.

Question 19

Explain what is meant by turgid or flaccid cells (in plants)

Answer 19

A turgid plant cell means that it is full of water. The pressure of water in cytoplasm against cell wall is called turgor pressure. Prevents more water entering plant by osmosis even if it is in a solution with a higher water concentration than in the cytoplasm. Prevents wilting of leaves.

A plant cell that is dehydrated is said to be plasmolysed. This is when the cytoplasm shrinks and the cell membrane pulls away from the cell wall leaving a gap between the wall and membrane. Leaves may wilt.

Question 20

Explain plant uptake of water

Answer 20

Plant roots absorb soil water through osmosis since water concentration is lower in cytoplasm. The water molecules travel further into the root tissue until water molecules reach xylem vessels. The water molecules transported towards leaves. Transpiration from leaves helps draw water up to maintain concentration gradient between root cells and xylem vessels.

Question 21

Explain effect of osmosis on animal cells

Answer 21

Animal cells also gain and lose water from osmosis. Effects can be more dramatic since they do not have a supporting cell wall. If you place an animal cell (e.g. red blood cell) into a solution of lower water potential, it will lose water by osmosis and become crenated.