B2.1 Supplying The Cell

Question 1

Describe what diffusion is

Answer 1

• Diffusion is the net movement of particles from a region of high concentration to a region of low concentration
• They move down a concentration gradient
• Energy is not transferred during diffusion, it is a passive process

Question 2

Where does diffusion occur in the body?

Answer 2

• Your blood transports glucose and oxygen around your body and they diffuse into the cells that need them
• Some chemical reactions make toxic waste products so they diffuse out of cells

Question 3

State three ways in which you can increase the rate of diffusion

Answer 3

• Decreasing the distance the particles need to move means that it takes less time for them to travel.
• Increasing the concentration gradient - The steeper the concentration gradient, the greater the net movement of particles.
• Increasing the surface area allows more space for diffusion, so more particles can move in a period of time.

Question 4

Describe what is meant by a concentration gradient

Answer 4

A concentration gradient exists when there is a region of high concentration leading to a region of low concentration:
- Going from high to low concentration is going down the concentration gradient.
- Going from low to high concentration is going against the concentration gradient.

Question 5

What is osmosis

Answer 5

• Osmosis is the net movement of water molecules across a partially permeable membrane from a region of higher water concentration, to a region of lower water concentration.

Question 6

How does water get into cells?

Answer 6

In order for water to get into cells, the water concentration inside the cell must be lower than that outside the cell. The water moves across a partially permeable membrane, going down the concentration gradient.

Question 7

Isotonic

Answer 7

• When the solute and water concentration in a solution are the same as the cell. There is no net movement of water across the cell membrane, and the cell maintains its normal shape and size.

Question 8

Hypertonic

Answer 8

Solution has a higher concentration of solute and lower concentration of water than the cell. This means tat when a cell is placed in a hypertonic solution, water will move out of the cell into the solution by osmosis because the cell has more free water. This causes the cell to become crenated.

Question 9

Hypotonic

Answer 9

Solution has a lower concentration of solute and high concentration of water than the cell. This means that when a cell is placed in a hypotonic solution, water will move out of the solution into the cell by osmosis because the solution has more free water. This causes the cell to swell and potentially burst.

Question 10

What is active transport?

Answer 10

The movement of molecules across a cell membrane, from a region of lower concentration to a region of higher concentration, and requiring energy from cellular respiration.

Question 11

How does the energy required during active transport come from the mitochondria?

Answer 11

Cellular respiration occurs in the mitochondria and energy is made. Mitochondria stores this energy in molecules called ATP, which takes the energy to parts of the cell that need it.

Question 12

Explain how root hair cells use active transport

Answer 12

Root hair cells use active transport to absorb mineral ions. They cannot use diffusion since there is a higher concentration of mineral ions inside the cell, so they need lots of energy for active transport. This is why root hair cells contain many mitochondria and have a large surface area.

Question 13

What is the cell cycle?

Answer 13

The process of cell growth and division. It is the life cycle of the cell.
It consists of three stages, DNA replication, movement of chromosomes, and division.

Question 14

Explain DNA replication (Interphase)

Answer 14

• the DNA molecule unzips forming two separate strands.
• the DNA bases on each strand are exposed, and free nucleotides in the nucleus line up against each of the strands following the rule of complementary base pairing.
• this forms DNA base pairs and when the whole strand is complete, there are two identical molecules of DNA.

Question 15

Explain mitosis

Answer 15

• the chromosomes line up across the centre of the cell - metaphase
• each chromatid is pulled to opposite ends of the cell by spindle fibres - anaphase
• nucleus forms around each set of chromosomes so two new nuclei are formed - telophase

Question 16

Explain cytokinesis

Answer 16

The cytoplasm and cell membranes divide to form two identical daughter cells

Question 17

What is mitosis?

Answer 17

Mitosis is the process by which body cells divide. Each cell divides to produce two identical daughter cells. They are genetically identical to the parent

Question 18

What are specialised cells

Answer 18

Specialised cells are cells that have a specific role in the body and to help them fulfil that role they have a specific shape or structure.

Question 19

Sperm cells

Answer 19

Specialised to transfer genetic material from the male to the ovum
- flagellum - whips from side to side to propel the sperm to the ovum.
- lots of mitochondria - reactions of respiration transfer energy from chemical stores so that the flagellum can move.
- acrosome - stores digestive enzymes which break down the outer layers of the ovum to allow the sperm to transfer and incorporate its genetic material.

Question 20

Fat cells

Answer 20

Specialised to store fats mean be used as a store of energy, enabling an animal to survive when food is short. Provide animals with insulation. Used to form a protective layer around some organs such as the heart.
- small layer of cytoplasm surrounding fat reservoir
- can expand up to 1000 times their original size as they fill with fat

Question 21

Red blood cells

Answer 21

Specialised to transport oxygen around the body
- biconcave discs - they are pushed in on both sides to form a biconcave shape which increases the surface area to volume ratio, speeding up the diffusion of oxygen into the cell and carbon dioxide out of the cell.
- full of haemoglobin - this protein binds to oxygen to form oxyhemoglobin which is also bright red.
- no nucleus which means that their is space to contain more haemoglobin molecules.

Question 22

Ciliated cells

Answer 22

You have these in your airways. In between these cells are goblet cells which produce sticky mucus. This traps dirt and bacteria. The cilia on top of the cells sweeps the mucus away from your lungs to the back of the throat and you then swallow it. Any bacteria present are killers in your stomach.

Question 23

Palisade cells

Answer 23

Specialised for carrying out photosynthesis. They are found near the surface of the leaf and are packed full of chloroplasts. They have a regular shape to allow close packing within the leaf, maximising the absorption of sunlight.

Question 24

What are stem cells?

Answer 24

Stem cells are undifferentiated cells. They divide by mitosis to form more cells which then differentiate and become specialised. This means that stem cells can develop into any type of specialised cell and therefore form all types of tissues and organs.

Question 25

Embryonic stem cells

Answer 25

They are found in embryos. They divide by mitosis to produce all the cells needed to make an organism. Embryonic stem cells have the ability to differentiate into all cell types.

Question 26

Adult stem cells

Answer 26

Found in various body tissues such as the brain, bone,p marrow, skin, and liver. They are able to differentiate into some different types of cells but not all.

Question 27

Meristems

Answer 27

Plants continue to grow throughout their lives, but only particular parts of the plant grow. These are called meristems. Stem cells are found in plant meristems. These cells look very different to normal plant cells, they are smaller, they have very thin walls, small vacuoles, and no chloroplasts.