2 & 3 - Cells & Biological Molecules

Question 1

What is the cytoplasm?

Answer 1

It’s found inside the cell and contains all the other cell structures.

Question 2

What is the cytoplasm’s function?

Answer 2

It supports cell structures, is the site of many chemical reactions, and contains water and many solutes.

Question 3

What is the nucleus and it’s function?

Answer 3

It’s surrounded by a nuclear membrane to separate it from the cytoplasm. It contains genetic material in chromosomes which control how cells grow and work, and controls cell division.

Question 4

What is the cell membrane and its function?

Answer 4

It surrounds the cell, holds it together and controls substances entering and leaving the cell.

Question 5

What is the cell wall and its function?

Answer 5

It’s made of cellulose and surrounds the cell membrane in plant cells, supports the cell and defines its shape.

Question 6

What are chloroplasts and their functions?

Answer 6

Chloroplasts are organelles found in the cytoplasm that are packed with the pigment chlorophyll and so are green in colour. It is the site of photosynthesis, provides food for plants, and the chlorophyll pigments absorb light energy needed for the reaction to occur.

Question 7

What are vacuoles and their function?

Answer 7

Vacuoles are large vesicles that take up a large part of the interior of plant cells. They contain cell sap, are used for storage of certain materials, and help support the shape of the cell.

Question 8

What is a root hair cell, its function and adaptations?

Answer 8

It absorbs water and mineral ions from soil. The root hair increases surface area of cell to ensure maximum absorption of water and mineral ions. Walls are thin to ensure water moves through quickly. No chloroplasts present.

Question 9

What is the palisade mesophyll cell, its function and adaptations?

Answer 9

It’s function is photosynthesis. Column shaped to maximise absorption of sunlight and fit as many in a layer under the upper epidermis of the leaf as possible. Contains many chloroplasts for maximum photosynthesis.

Question 10

What is a ciliated cell, its function and adaptations?

Answer 10

It moves the mucus in the trachea and bronchi. Extensions of the cytoplasm at the surface of the cell form hair-like structures called Cilia which beat to move mucus and trapped particles up to the throat.

Question 11

What is a red blood cell, its function and adaptations?

Answer 11

It transports oxygen. It’s a biconcave shaped disc, as it increases the surface area for mor efficient diffusion of oxygen. It contains haemoglobin which joins with oxygen to transport it. It contains no nucleus to increase the space available for haemoglobin inside.

Question 12

What is a sperm cell, its function and adaptations?

Answer 12

It’s function is reproduction. The head contains the genetic material for fertilisation in haploid nucleus (containing half the normal number of chromosomes). The acrosome in the head contains digestive enzymes so that a sperm can penetrate an egg. The mid-piece is packed with mitochondria to release energy needed to swim and fertilise the egg. The tail enables the sperm to swim.

Question 13

What is an egg cell, its function and adaptations?

Answer 13

It’s function is reproduction. It contains a lot of cytoplasm which has nutrients for the growth of the early embryo. Haploid nucleus contains the genetic material for fertilisation. Cell membrane changes after fertilisation by a single sperm so that no more sperm can enter.

Question 14

What is diffusion?

Answer 14

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 15

How do substances move in and out of the cell?

Answer 15

Through Diffusion.

Question 16

What is osmosis?

Answer 16

Osmosis is the diffusion of water molecules from a dilute solution (high concentration of water) to a more concentrated solution (low concentration of water) across a partially permeable membrane.

Question 17

What are the factors that influence diffusion?

Answer 17

Surface area, Distance, Temperature, and Concentration gradients.

Question 18

How does surface area influence diffusion?

Answer 18

The bigger a cell or structure is, the smaller its surface area to volume ratio is, slowing down the rate at which substances can move across its surface. Many cells that are adapted for diffusion have increased surface area.

Question 19

How does temperature influence diffusion?

Answer 19

The higher the temperature, the faster molecules move as they have more energy. This results in more collisions against the cell membrane and therefore a faster rate of movement across them.

Question 20

How does distance influence diffusion?

Answer 20

The smaller the distance molecules have to travel, the faster transport will occur. This is why blood capillaries and alveoli have walls which are only one cell thick, ensure the rate of diffusion across them is as fast as possible.

Question 21

How does concentration gradient influence diffusion?

Answer 21

The greater the difference in concentration either side of the membrane, the faster movement across it will occur. This is because on the side with the higher concentration, more random collisions against the membrane will occur.

Question 22

Why is osmosis important for plant tissues?

Answer 22

Water moves into the cell, the vacuole gets bigger and pushes the cell membrane against the cell wall. Water entering the cell by osmosis makes the cell rigid. This provides strength and support for the plant. Pressure created by cell wall stops too much water entering and prevents cell from bursting.

Question 23

What is turgor pressure?

Answer 23

The pressure of the cytoplasm pushing against the cell wall.

Question 24

How do plant cells prevent themselves from bursting with excess water?

Answer 24

The high turgor pressure prevents any more water entering the cell by osmosis, even if it’s in a solution that has a higher water potential than inside the cytoplasm of the cells. The water then moves across the cell membrane of root hair cells into the root by osmosis until the xylem, then they are transported away from the root by the transpiration stream.

Question 25

What occurs when cells are plasmolysed?

Answer 25

The cell membrane has pulled away from the cell wall. E.g. When water molecules move out of potato cells by osmosis, leaving them flaccid (floppy)

Question 26

What does higher and lower water potential mean?

Answer 26

A region of higher water potential is a dilute solution and lower water potential is a concentrated solution.

Question 27

How does osmosis occur in plant tissues?

Answer 27

As animal cells don’t have a supporting cell wall, the results are more severe. If an animal cell is placed into a solution with lower water potential than the cell, it’ll lose its water by osmosis and become crenated (shrivelled up). If an animal cell is placed into a solution with higher water potential than the cell, it’ll gain water by osmosis and since it has no cell wall to create turgor pressure, it’ll continue this till the cell membrane is stretched and bursts.

Question 28

What chemical elements make up carbohydrates?

Answer 28

Carbon, oxygen and hydrogen.

Question 29

What chemical elements make up proteins?

Answer 29

All contain carbon, oxygen, hydrogen and nitrogen, and some contain small amounts of other elements like sulphur.

Question 30

What chemical elements make up lipids?

Answer 30

Carbon, oxygen and hydrogen.

Question 31

What does a group of glucose molecules form?

Answer 31

Starch, glycogen or cellulose.

Question 32

What does a group of amino acids joined together form?

Answer 32

A Protein.

Question 33

What do fatty acids and glycerol form?

Answer 33

1 glycerol molecule chemically bonded to 3 fatty acid chains forms fats and oils.

Question 34

What is the test for glucose? (explain)

Answer 34

Benedict’s test.

1. Add Benedict’s solution into sample solution in test tube.
2. Heat at 60 – 70 °c in water bath for 5 minutes
3. Take test tube out of water bath and observe the colour
4. A positive test will show a colour change from blue to orange or brick red

Question 35

What is the test for starch? (explain)

Answer 35

The iodine test.

1. Add drops of iodine to the food sample
2. A positive test will show a colour change from orange-brown to blue-black.

Question 36

What is the test for protein? (explain)

Answer 36

The Biuret solution.

1. Add drops of Biuret solution to the food sample
2. A positive test will show a colour change from blue to violet/purple

Question 37

What is the test for lipids?

Answer 37

The ethanol test.

1. Food sample is mixed with 2cm³ of ethanol and shaken.
2. The ethanol is added to an equal volume of cold water
3. A positive test will show a cloudy emulsion forming.

Question 38

Why is water important as solvent?

Answer 38

Water is important for all living organisms as many substances are able to dissolve in it (is a solvent)