Cell Biology AQA GCSE Biology

Name the two main types of cell.

Prokaryotic, eukaryotic

Name the two main types of eukaryotes

Plants, animals

Name 3 organelles ALL eukaryotes have.

Cell membrane, cytoplasm, nucleus

Name one type of prokaryote.

Bacteria

Name three organelles prokaryotic cells ALWAYS have

Cell membrane, cytoplasm, cell wall

How is DNA stored in prokaryotic cells?

All DNA is found in a single loop, and there may be one or more smaller rings or DNA called plasmids.

How large are plant cells? Give your answer in micrometers.

10-100 micrometers

How large are animal cells? Give your answer in micrometers

10-30 micrometers

How large are bacterial cells? Give your answer in micrometers

0.2-2 micrometers

What does centi- mean?

x10^-2

What does milli- mean?

x10^-3

What does micro- mean?

x10^-6

What does nano- mean?

x10^-9

What do nuclei do, and what does it contain?

They contain DNA which controls the cell

What do cell membranes do?

They control what enters and leaves the cell

What do mitochondria do and what do they contain?

They contain enzymes that allow aerobic respiration to occur

What do chloroplasts do and what do they contain?

They contain enzymes and chlorophyll that allow photosynthesis to occur

What do plasmids do and what do they contain?

They contain DNA that enhances the survival of an organism.

What do cells walls do and what do they contain?

They contain cellulose that strengthens the cell.

What do permanent vacuoles do and what do they contain?

They contain cell sap that keeps the cell turgid

What does cytoplasm do and what does it contain?

It contains enzymes which allow chemical reactions to take place in the cell

What do ribosomes do and what do they contain?

They contain enzymes which allow protein synthesis to occur

What 5 organelles do most animal cells contain?

Nucleus, Cytoplasm, Cell Membrane, Mitochondria, Ribosomes

What 3 organelles do plants often have that animal cells don't.

Chloroplasts, Permanent Vacuole, Cell Wall

On an image of a plant cell, what are the two outermost organelles called, in order of outermost to innermost?

Cell Wall, then Cell Membrane

On an image of a plant cell, what are two large circles/rectangles inside the cell called, in order of largest to smallest?

Permanent Vacuole, then Nucleus

On an image of a plant cell, what are the two types of very small but visible "dots" in the cell called, starting with the organelle only present in plants?

Chloroplasts, then mitochondria

On an image of a plant cell, what is the space inside of a cell called? What is the name of the organelle that usually cannot be seen on a diagram of a cell?

Cytoplasm, then ribosomes

For the Microscopy Practical, how do you focus on the slide?

Use the lowest power objective lens. Slowly turn the course focusing wheel until the cells come into focus, then use the fine focusing wheel to make the focus perfect,

For the Microscopy Practical, how do you include a magnification scale?

Put a clear ruler in view of the microscope. On your drawing, put a line representing one millimetre. This is a scale bar. Include a magnification.

For the Microscopy Practical, how would you prepare a microscope slide of onion epidermal cells?

Using forceps, peel a thin layer of cells from an onion which has been cut in half with a knife. Place these cells on a slide, add a drop of iodine stain, and using clean forceps put a coverslip over the cells without trapping air bubbles. Place this slide on the microscope stage.

How are sperm cells adapted to their function? Explain four ways.

They have an acrosome which contains enzymes which break down an egg's wall. They also contain half the amount of chromosomes in the nucleus so that when it fertilises an egg the embryo has one full set of DNA. They contain many mitochondria to provide the cell with enough energy to swim towards the egg, and they a flagellum which makes the cell streamlined so it can swim to the egg faster.

How are nerve cells adapted to their function? Explain three ways.

They have a long thin axon, which allows electrical signals to travel very fast without hitting a synapse. They have an insulating myelin sheath which makes the signal travel faster, and they have many dendrites so they can receive signals from many cells.

How are muscle cells adapted to their function? Explain three ways

They are long so can slide over each other easily. They contain lots of mitochondria so the cell has enough energy to contract to cause movement. They contain glycogen which can be converted to glucose for respiration so the cell can contract to cause movement.

How are root hair cells adapted to their function? Explain four ways.

They have a large protrusion which increases surface area so diffusion and osmosis is faster. They have a large permanent vacuole that stores water so there is a larger water concentration gradient for osmosis. They have many mitochondria to provide energy for active transport. They have no chloroplasts to make room for other organelles and because there is no light for photosynthesis underground.

How are xylem cells adapted to their functions? Explain three ways.

They are hollow which allows them to transport water up and down the cell. They contain lignin which strengthens the cell so they can withstand water pressure, and they are dead so they do not use up unnecessary nutrients.

How are phloem cells adapted to their function? Explain two ways.

They have sieve plates which allows them to form tubes which sugar can be transported. They also have almost no organelles so that there is more room for dissolved substances to be transported. This means that the cell must have companion cells to provide it with nutrients.

Explain the importance of cell differentiation.

It allows unspecialised stem cells to become specialised cells, and it allows cells to perform specific functions. This makes it important for growth and development of embryos and seedlings, and for repair of blood and plant tissue.

When do cells differentiate in animals?

At an early stage.

When do cells differentiate in plants?

They retain the ability to differentiate throughout life.

Explain what happens during cell differentiation?

It acquires different sub-cellular structures to enable it to carry out a certain function.

How have microscopy techniques developed over time?

Light microscopes were invented hundreds of years ago. Light microscopes have developed to be easier to use and have a higher magnification. The invention of electron microscopes increased magnification and resolution.

Explain how electron microscopy has increased understanding of sub-cellular structures.

Light microscopes have limited magnification and resolution, and as such cannot see certain sub-cellular structures in detail, such as ribosomes. The electron microscope has a higher magnification and resolution, so can therefore see these sub-cellular structures in lots of detail.

What equation links image size, magnification and real size?

Magnification = image size / real size

How do bacteria divide? Describe the optimum conditions and the optimum rate.

Binary fission - this happens once every 20 minutes if they have enough nutrients and a suitable temperature.

Name two mediums in which bacteria can be cultured.

Nutrient broth solution, agar gel plate.

Give one use of culturing micro-organisms.

Investigating the action of disinfectants and antibiotics.

What equation links bacteria at start, bacteria in a population, mean division time and time taken?

Bacteria in a population = Bacteria at start x 2 ^ (time taken/mean division time)

What equation links area of a circle and the radius of a circle?

Area of a circle = pi x radius^2

For the Binary Fission required practical, how would you prepare an uncontaminated culture? Explain how each step prevents contamination.

First, the Petri Dish, medium culture (agar gel/nutrient broth) and inoculating loop must be sterilised since they may contain microorganisms that could contaminate the cultures. Inoculating loops can be sterilised using a flame. Then, the inoculating loop should be used to transfer micro-organisms from source to the medium. Then, the lid of the the Petri Dish should be secured with adhesive tape to prevent other micro-organisms entering and contaminating the sample. The Petri dish should be stored upside-down and, in school labs, at 25°C to prevent condensation causing contamination and to prevent the micro-organisms from mutating into potentially harmful pathogens.

For the Binary Fission required practical, how would you test the effectiveness of liquid antibiotics? How would you determine which antibiotic was the most effective?

Place one small piece of tissue paper into one of the antibiotic that you want to test so that the tissue is soaked with antibiotic. Repeat for each antibiotic, and for control purposes soak one piece of tissue paper with water. Place each piece of tissue paper using forceps into the inoculated medium. Wait one day for the bacteria to multiply. What should happen is that each piece of tissue paper except the control should have a clear circle around them where no bacteria can survive. Calculate the area of each zone of inhibition. The antibiotic with the largest zone of inhibition is the most effective against this bacteria.

Order these in order of size, largest to smallest: Cell, chromosome, DNA, gene, nucleus.

Cell, nucleus, chromosome, gene, DNA

True or false: In body cells the chromosomes are normally found in pairs.

True

What are the three phases of the cell cycle?

Interphase, mitosis, cytokinesis

Briefly, what happens in the cell cycle?

The genetic material is doubled and then the cell divides into two identical cells.

What happens during interphase?

The cell grows, the number of sub-cellular structures increases such as ribosomes and mitochondria, and the DNA replicates to form two copies of each chromosome.

What happens during mitosis?

One set of chromosomes is pulled to each end of the cell and the nucleus divides.

What happens during cytokinesis?

The cytoplasm ad cell membrane divide to form two identical cells.

Why is mitosis important?

Growth and development of multicellular organisms

What is a stem cell?

An undifferentiated cell of an organism which is capable of giving rise to many more cells of the same type, and from which certain other cells can arise from differentiation.

Describe the function of stem cells in embryos.

They can divide and can differentiate into most types of human cells, allowing growth and development.

Describe the function of stem cells in adults.

They can differentiate into blood cells, replacing blood cells when blood cells die.

Describe the function of meristem cells in plants.

They can differentiate into any type of plant cell throughout the life of the plant, making them useful for growth and repair.

Where are stem cells found in adults?

The bone marrow

What are stem cells in plants called?

Meristem cells

Name two diseases that could be cured by stem cells.

Diabetes and paralysis

How does therapeutic cloning work?

An embryo is produced with the same genes as the patient

Evaluate the use of stem cells in medical research and treatments. Do not give your own opinion.

Embryonic stem cells can differentiate into any type of cell. They could be used to treat previously untreatable diseases. They will not be rejected or provided by therapeutic cloning. However, there is a risk of the transfer of viral infection. It could be seen as unethical since it is destroying potential life. Many religions also forbid abortion, and therefore cannot use embryonic stem cells.

Give two uses of meristem cells.

Rare species can be cloned to protect from extinction, crops with special features such as disease resistance can be cloned to produce large numbers of identical plants for farmers.

What is diffusion?

Diffusion is the spreading out of the particles in a substance in solution or in a gas, resulting in a net movement from an area of high concentration to an area of low concentration.

Name 6 places where diffusion occurs in biology and state what diffuses in each case.

It occurs in the small intestine, where glucose, amino acids, fatty acids and glycerol diffuse into the bloodstream. It also occurs in most body cells where urea moves into the bloodstream. It occurs in the alveoli of the lungs, the gills of fish and the leaves of plants, where oxygen moves to the blood/gills/leaf and carbon dioxide moves to the lungs/water/air. It occurs in the roots of a plant, where water and mineral ions enter the root.

Explain three factors that affect the rate of diffusion.

A higher concentration gradient increases the rate of diffusion because there are many particles that can move to a lower concentration while there are no particles that could do the reverse, so the net movement is faster. A higher temperature leads to diffusion occurring faster since this means particles have more energy so the movement of particles is faster. A higher surface area of a membrane means that there are more places where diffusion can occur across, so diffusion happens faster.

Explain why multicellular organisms need exchange surfaces and transport systems while single-celled organisms don't.

A single-celled organism has a relatively high surface area to volume ratio. This allows sufficient transport of molecules into and out of the cell to meet the needs of an organism. On the other hand, a multicellular organism has a relatively low surface area to volume ratio. This means that in order for there to be sufficient transport of molecules into and out of the organism to meet its needs, they must have exchange surfaces and transport systems.

Name four ways the effectiveness of an exchange system can be increased, giving up to 5 examples of each.

Having a large surface area, such as the microvilli in the small intestine, the alveoli in the lungs, the gills of fish, the thin leaves of plants and protrusions in root hair cells. Having a thin membrane, such as capillaries being one cell thick, the waxy cuticle and stomata being very thin in a leaf, and root hair cells being small. Having an efficient blood supply through capillaries. Being ventilated during gaseous exchange.

What is osmosis?

The diffusion of water from an area of high water concentration to an area of low concentration gradient through a partially permeable membrane.

For the Osmosis required practical, how and why do we prepare the potato before placing them in test tubes?

First, we peel the potato since the skin interferes with osmosis. Next, we use a cork borer to produce cylinders of potato, and then use a scalpel to make each cylinder the same length. This is so each cylinder has the same surface area and volume. We measure the length and mass of each cylinder using a ruler and a balance

For the Osmosis required practical, why is distilled water used?

As a control variable - also, tap water contains dissolved ions that could affect rate of osmosis.

For the Osmosis required practical, how and why do we remove excess water

Using a paper towel - it prevents the extra mass of the water affecting the results.

What is active transport?

The movement of substances from an area of low concentration to an area of high concentration against a concentration gradient, which requires energy from respiration.

Name two places active transport takes place in biology and state what is actively transported in each case.

Small intestine - glucose moves to the blood

Root hair cells - mineral ions move from the soil

Explain the differences between diffusion, osmosis and active transport.

Diffusion and osmosis are passive processes where substances are moved down a concentration gradient, while active transport is an active process that moves substances against a concentration gradient. Diffusion and Active transport can move any substances and do not require a partially permeable membrane, while osmosis can only move water and requires a partially permeable membrane.