GCSE Biology Revision

CELL BIOLOGY

Topic 1

What are Cells?

Cells are the basic unit of living organisms. They provide structure and carry out certain functions.

What are the 2 types of cells?

Eukaryotic and Prokaryotic

Compare Eukaryotic and Prokaryotic cells.

Eukaryotic:

• Contains a nucleus

• Found in plants, animals and fungi

• 10-100 micrometres in size

Prokaryotic:

• Does NOT contain a nucleus

• 0.1-5.0 micrometres in size, much smaller than eukaryotic

• Bacteria are prokaryotes

Name the properties of Prokaryotes.

• No mitochondria or chloroplasts

• Single DNA loop: most of their DNA is stored in a single loop stored within their cytoplasm

• Plasmids: some bacteria cells contain small rings of DNA called plasmids.

What are the sub-cellular structures of animal cells?

• Cell membrane - controls what enters and exits the cell

• Nucleus - contains chromosomes where the genetic material is stored

• Ribosomes - responsible for making proteins

• Mitochondria - where aerobic respiration takes place

• Cytoplasm - where most of the cell’s chemical reactions take place

What ADDITIONAL sub-cellular structures do plant cells have?

• Permanent vacuole - a fluid-filled sac that stores water

• Chloroplasts - contains chlorophyll, which is needed for the process of photosynthesis

• Cell wall - surrounds the cell and is made of cellulose. Increases the structural strength of the cell

Describe cell differentiation in Animals and Plants.

When cells differentiate, they acquire different sub-cellular structures. CD happens at different stages of development in plants and animals.

Plants:

• Many plant cells can differentiate throughout their lives

• This means that plants are always able to create new tissues

Animals:

• Most animal cells differentiate early on in their development

• New tissues are rarely created by cell differentiation

What are the sub-cellular structures of Bacterial cells?

• Cell wall

• Cell membrane

• Cytoplasm

• Flagella

• Plasmids

Describe cell specialisation in Sperm cells. (animal cells)

Sperm cells are specialised (perform a specific function). Sperm cells are specialised to fertilise egg cells. To do this, they need to travel long distances relative to their size.

• Head

  • The ‘head’ contains the sperm cell’s nucleus. The nucleus carries one half of an organism’s genetic material.

  • This combines with the egg cell's half of genetic material to fertilise the egg cell.

• Acrosome

  • The acrosome is found at the tip of the head. It contains the digestive enzymes needed to penetrate (break into) an egg cell.

• Middle section

  • The middle section is filled with mitochondria to provide the sperm with the energy it needs to travel a long distance to reach the egg cell.

• Flagellum

  • The flagellum (‘tail’) is used for the cell’s motion. This allows sperm cells to travel towards the egg cell.

Describe cell specialisation in Nerve cells. (animal cells)

• Axon

  • Part of the cell that electrical signals travel along.

  • Nerve cells have a long axon. This increases the distance that electrical signals can travel.

• Myelin sheath

  • A sheath made of a material called myelin surrounds the axon of the nerve cell. This stops the electrical nerve signals leaking out of the nerve cell.

  • This increases the speed of transmission (travel) of electrical signals.

• Dendrites

  • Branches of a nerve cell.

  • Several dendrites spread outwards from the cell body to transfer electrical messages to other neurons.

  • Electrical messages travel between neurons at synapses.

Describe cell specialisation in Muscle cells. (animal cells)

Muscle cells are specialised (perform a specific function). They can produce force and motion.

• Mitochondria

  • A muscle cell contains lots of mitochondria to generate lots of energy for motion.

• Protein fibres

  • Protein fibres within the cell can contract, allowing the muscle to move.

Describe cell specialisation in Root Hair cells. (plant cells)

Root hair cells are specialised (to perform a specific function). Their structure allows the plant to absorb more water. They also allow a plant to take in the minerals it needs to survive.

• No chloroplasts

  • These cells are located underground.

  • This means that they do not contain chloroplasts (there is no light for photosynthesis).

• Long projections

  • Root hair cells have long projections that increase the surface area that the plant can use to absorb water and minerals.

Describe cell specialisation in Xylem cells. (plant cells)

The xylem is specialised to transport water up the stem of a plant and into the leaves.

Open ended cells

• Xylem vessels are made up of a series of connected dead xylem cells.

• The end walls of the DEAD cells are broken to allow WATER to move through.

Lignin

• Lignin strengthens the cell walls of xylem cell

Describe cell specialisation in Phloem cells. (plant cells)

The phloem is specialised to transport food products to parts of the plant where they are needed. Phloem vessels are made up of columns of LIVING cells.

• Small holes

  • The end walls of phloem cells contain small holes to allow FOOD products to move up and down the phloem vessels throughout the plant.

Which 2 variables matter most in Magnification?

• Magnification

  • Magnification tells us how many times larger an image seen through a microscope is compared to the real object.

• Resolution

  • Resolution is the ability to distinguish between (tell apart) two or more objects that are close together.

State the equation of Magnification.

Magnification = image size ÷ actual size

Evaluate uses of Light and Electron Microscopes.

Light:

• Allowed bacteria to be seen for the first time

• Allowed us to see plant and animal cells as separate objects

• However, we still could not tell lots of sub-cellular (within the cell) structures apart.

Electron:

• The high level of detail allowed scientists to see sub-cellular structures more clearly

• Allowed scientists to study how structures such as mitochondria, chloroplasts, and ribosomes function

Describe the Required Practical of Microscopy!!!!

1. Put a thin sample of tissue (e.g. onion epidermis) onto a microscope slide.

2. Add a few drops of a suitable stain/dye (e.g. iodine).

3. Place a cover-slip on top of the tissue and place the slide onto the microscope stage.

4. Use the objective lens with the lowest magnification, and focus on the sample.

5. Increase the magnification and refocus to see different features of the cell.

Where can antibiotics be safely grown?

• Agar gel plates

• Nutrient broth

Describe the Risks, Sources, and Prevention of Contamination.

When growing cultures of bacteria, we provide conditions that are good for lots of different types of bacteria to grow. If bacteria that are not being investigated grow, then our investigation has been contaminated.

• Risks: as well as jeopardising the investigation, contamination is a serious health issue as well

• Sources: Air, Skin, Soil, Water

• Prevention: the cultures must be pure (do not contain bacteria that is not being investigated)

How can we prevent contamination?

Aseptic Technique:

To prevent contamination (from skin, air, soil, or water), aseptic (free from contamination) techniques are used on all apparatus. These techniques kill and prevents the entry of unwanted bacteria. They involve:

• Flames

• Boiling

• Lids - on petri dishes and use adhesive tape so bacteria can’t enter

• Temperature - schools grow bacteria in maximum 25 degrees Celsius so no harmful bacteria can grow.

What is the equation for calculating the Area of a Circle?

Area = π x radius².

What are Chromosomes made of?

Chromosomes

Chromosomes are made from molecules of DNA and can be found in the nucleus of a cell. Each chromosome carries a large number of genes. Chromosomes are typically found in pairs in body cells.

Describe the process of The Cell Cycle.

The cell cycle is the series of events involved in cell growth and cell division. It involves mitosis (a type of cell division), which allows for the growth, repair and asexual reproduction of cells. It involves:

Initial growth stage

• Extra ribosomes, mitochondria and other sub-cellular structures are produced.

• The cell’s chromosomes are replicated so that there are two sets of the cell’s chromosomes.

Mitosis

• The two sets of chromosomes are pulled to opposite ends of the cell.

• Then, the nucleus divides into two.

Cell division

• The cytoplasm and cell membranes are divided resulting in the production of two identical cells.

Describe the process of Mitosis.

Mitosis (a type of cell division) is part of the cell cycle. During mitosis:

Chromosomes are pulled apart

• The two sets of chromosomes copied during the initial growth stage are pulled to opposite ends of the cell.

Nucleus divides

• The nucleus divides into two.

Identical daughter chromosomes

• Mitosis ensures that both daughter cells have the same chromosomes as each other and the parent cell.

• This is important for processes that require identical cells to be produced.

What are Stem Cells?

Stem cells are undifferentiated cells that have not yet specialised to perform a specific function. They can create more stem cells or differentiate (become another type of body cell) to perform a function. Stem cells can be found in:

• Embryos - these stem cells can differentiate into most cell types, to produce all of the cell types that make up an organism.

• Bone Marrow - In human adults, stem cells can be found in bone marrow

• Plant Meristems - plant stem cells are found in the meristem tissue. Plant stem cells can differentiate into all types of plant cell throughout the life of the plant. This allows plants to grow for their whole lives

What are some uses of Stem Cells?

• Stem cell treatments - may be able to replace damaged cells in the body

• Plant clones - can help us quickly and cheaply produce cloned plants

• Therapeutic cloning - a produce that produces an embryo with genes that are identical to the patient’s

Name 2 advantages of Stem Cells

• Could transmit viral infections

• Ethical and Religious beliefs: they believe that life starts at conception, so the embryo is alive and this is ‘killing’.

What is Diffusion?

Diffusion is the random movement of particles through a gas or liquid from high concentration to a low concentration.

Name 3 factors affecting Diffusion.

The rate of diffusion can speed up or slow down based on the following factors:

• Concentration gradient - The concentration gradient is linked to the difference in concentration between two areas.

• Temperature - The higher the temperature, the faster the rate of diffusion.

• Membrane Surface Area - The larger the surface area of the membrane that a substance is diffusing through, the faster the rate of diffusion.

What are Exchange Surfaces and what adaptations do they have?

Exchange surfaces are surfaces that are adapted to maximise the efficiency of gas and solute exchange across them. They have the following adaptations:

• Large Surface Area - allows more of a substance to diffuse at the same time

• Thin Membrane - reduces the diffusion distance

• Blood supply

• Ventilation

Name 5 examples of Exchange Surfaces.

• Small intestine - adapted for exchanging nutrients

• Lungs - adapted for exchanging carbon dioxide and oxygen between the blood and air

• Gills - adapted for exchanging oxygen that is dissolved in water

• Roots - adapted for taking up both water and minerals from the soil around them.

• Leaves - adapted for exchanging carbon dioxide and oxygen between the leaves and the surrounding air.

What is osmosis?

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

• Partially permeable membrane - is required for osmosis, allows water through, but won't let larger molecules dissolved in water pass through.

• Water movement - Water will move to make the concentrations the same on both sides of the membrane

• Net movement of water

Describe the Required Practical of Osmosis in Plant Tissue!!!!!!!

1. Cut potato cylinders to equal sizes and shapes.

2. Measure their initial mass and length.

3. Place each cylinder into test tubes with different concentrations of salt or sugar solution.

4. Leave for a fixed time.

5. Remove cylinders, pat dry, and re-measure the mass and length.

6. Record all measurements in a table.

What is Active Transport important for in Plants and Animals?

• Sugar absorption in human gut

• Mineral absorption in plants

Describe Active Transport.

Active transport is the net movement of particles against a concentration gradient.

• This means that energy (ATP) is needed for active transport to happen.

Outline the differences between Active Transport, Osmosis, and Diffusion.

• Diffusion - Particles go DOWN the concentration gradient (high to low)

• Osmosis - Water only through a partially permeable membrane (type of diffusion)

• Active Transport - Uses ATP to move particles AGAINST the concentration gradient (low to high)