B1 - Cell Biology

What are Cells

Cells are the basic units of all living organisms.

What is a eukaryotic cell?

A eukaryotic cell is a type of cell that contains a nucleus.

They are usually animal or plant cells.

What is a prokaryotic cell?

A cell that does not contain a nucleus; genetic material is in a single DNA loop

They are usually bacteria cells.

What sub-cellular structures do most animal cells have?

Nucleus

Cytoplasm

Cell membrane

Mitochondria

Ribosomes.

What additional parts do plant cells have?

Cell wall

Chloroplasts

Permanent Vacuole

What is the function of the nucleus?

Contains genetic material and controls the activities of the cell

What is the function of mitochondria?

Site of aerobic respiration, releasing energy for the cell.

What is the function of ribosomes?

Site of protein synthesis

What is the function of the cell membrane?

Controls the movement of subsatnces in and out of the cell.

What is the function of the cytoplasm?

A gel - like substance where the chemical reactions occur.

What is the function of the cell wall?

Made of cellulose – provides structural support for the cell and maintains its shape

What is the function of chloroplasts?

Contain a green pigment, chlorophyll, for photosynthesis

What is the function of the permanent vacuole?

A large sac filled with cell sap to help keep cell turgid.

What is the genetic material in bacterial cells?

A single DNA loop and small rings of DNA called plasmids

Why are electron microscopes better than light microscopes?

They have a higher magnification and higher resolution,

How do you calculate magnification?

Magnification = image size / real size

Why do we stain specimens under a microscope?

To make structures more visible

What is cell differentiation?

When cells differentiate to become specialised to perform particular functions

When does differentiation mainly occur in animals?

At an early stage of development

When can plant cells differentiate?

Throughout their life

Explain how a sperm cell is adapted for its function

Tail - Enables sperm to swim

Many Mitochondria – Provides lots of energy

Contains enzymes – Penetrates the egg’s outer membrane

Explain how a nerve cell is adapted for its function.

Long axons - carries impulses over long distances

Myelin Sheath – Fatty layer that insulates the axon, speeding up the transmission of impulses.

How is a muscle cell adapted for its function?

Lots of mitochondria and fibres to contract.

How is a root hair cell adapted for its function?

Large surface area to absorb water and minerals.

Mitochondria – Provides energy for active transport.

How are xylem cells adapted for their function?

Hollow tubes - Allows efficient transport of water and minerals up the plant

The walls are strengthened with lignin, and it prevents collapsing under pressure.

What are chromosomes made of?

DNA molecules 

How many pairs of chromosomes are in human body cells?

23 pairs.

What happens during the interphase?

The cell grows and increases the amount of subcellular structures such as mitochondria and ribosomes.

DNA is replicated to form 2 sets of chromosomes

What happens during Mitosis?

Chromosomes line up at middle of the cell and they are pulled to the  opposite ends of the cell.

The nucleus divides.

What happens during cytokinesis?

The cell membrane and cytoplasm divide, forming two genetically identical cells.

Why is mitosis important

For growth, replacement of damaged cells, and asexual reproduction.

What are stem cells?

Undifferentiated cells that can develop into any type of cell

Where are stem cells found in humans?

Embryos and adult bone marrow

Where are stem cells found in plants?

Meristems

What can embryonic stem cells differentiate into?

Any type of cell

What can bone marrow stem cells differentiate into?

Blood cells such as Red Blood Cells, White Blood Cells, and Platelets

How can stem cells be used medically?

They can treat conditions such as paralysis and diabetes.

Why might some people be opposed to the use of human embryos in stem cell research?

• An embryo has the potential for life, so destroying it is morally wrong.

• Some religions see life beginning at conception, so using embryos for research may be seen as ending a human life.

What is therapeutic cloning?

Producing an embryo with the same genes as a patient to avoid rejection by the  immune system.

What are the risks of using stem cells?

Transfer of viral infections.

Also ethical/religious concerns

How can plant stem cells be used in agriculture

To clone plants quickly and protect rare species.

What is diffusion?

The movement of particles from an area of high concentration to an area of low concentration.

(Doesn’t require energy)

What factors affect the rate of diffusion ?

Concentration gradient, temperature, and surface area.

Name three substances that can diffuse through the cell membrane and two that can’t.

Can:
Oxygen, Carbon Dioxide, Water

Can’t:
Starch
Proteins

Why don’t single-celled organisms need transport systems?

Large surface area to volume ratio.

Why do multicellular organisms need transport systems?

Small surface area to volume ratio.

What is osmosis?

The movement of water from an area of high concentration to an area of low concentration through a semi-permeable membrane.

(From dilute to concentrated solution)

(Also doesn’t require energy)

Why do plant cells become turgid in pure water?

Water enters by osmosis, filling the vacuole and pushing on the cell wall.

What is active transport?

The movement of substances from an area of low concentration to an area of high concentration against the concentration gradient.

(Uses energy from respiration)

Where does active transport occur in plants?

In root hair cells which absorb mineral ions.

Where does active transport occur in animals?

In the small intestine, it absorbs glucose into the blood.

How does active transport differ from diffusion and osmosis?

It requires energy.

Give three adaptations of exchange surfaces that increase the efficiency of diffusion.

Large Surface Area – More particles to diffuse at once

Thin Membrane - Short diffusion distance

Good blood supply/ventilation – Maintains a steep concentration gradient

Give two ways that the villi in the small intestine are adapted for absorbing digested food.

1. Large surface area to increase rate of absorption.

2. Good blood supply to maintain a steep concentration gradient.

What is the aim of the microscopy required practical?

To use a light microscope to observe, draw and label a selection of plant and animal cells

How do you prepare a slide of onions?

1. Peel a thin layer of onion epidermis

2. Place it on a glass slide.

3. Add a drop of iodine solution to stain the cells

4. Carefully lower slip to avoid air bubbles

5. Place slide on microscope stage
   
   Make sure to start on the lowest power objective lens

How do you calculate the total magnification of a light microscope?

Total magnification = Eyepiece lens magnification × Objective lens magnification

How do you estimate the size of a cell using the microscope?

1. Measure field of view with a ruler

2. Estimate how many cells fit across the diameter.

3. Divide the diameter of cells by the number of the cells to get and approximate size.

What is the aim of the osmosis practical?

To investigate how different concentrations of a solution (salt or sugar) affect the mass of plant tissue.

What is the method for the osmosis practical?

1. Cut the potato into equal-sized cylinders.

2. Measure and record their initial mass.

3. Place each cylinder into solutions of different concentrations of sugar/salt.

4. Leave them in for around 20-30 minutes or up to 24 hours.

5. Take them out, and use a paper towel to remove any excess solution.

6. Measure the potato again and record the final mass

7. Calculate percentage change in mass.

How is percentage change calculated?

Percentage change in mass = (Final mass - Initial mass / Initial mass) x 100

What results would you expect?

In distilled water, water enters the potato cells → mass increases → cell becomes turgid.

In high sugar solution (low water concentration), water leaves potato cells → mass decreases → cell becomes flaccid.