cell biology

What is the function of the nucleus in a eukaryotic cell?

It contains the genetic material (DNA) and controls the cell's activities.

What is cytoplasm?

A jelly-like material where many chemical reactions happen and organelles are contained.

What is the role of the cell membrane?

It controls the movement of substances in and out of the cell.

Where does most energy release from respiration occur in a cell?

In the mitochondria.

Protein synthesis occurs in which tiny organelles?

Ribosomes.

What three structures are found in plant cells but not in animal cells?

A cellulose cell wall, a permanent vacuole, and chloroplasts.

What is the function of the cellulose cell wall in plant cells?

It strengthens and supports the cell.

What is the function of chloroplasts?

They are the site of photosynthesis, containing chlorophyll to absorb light energy.

What is contained within the permanent vacuole of a plant cell?

Cell sap, a solution of sugars, salts, and amino acids.

How does the genetic material in a prokaryotic cell differ from that in a eukaryotic cell?

In prokaryotes, the genetic material is not enclosed in a nucleus, consisting of a single DNA loop and sometimes plasmids.

What are plasmids?

Small rings of DNA found in the cytoplasm of prokaryotic cells, separate from the main chromosomal DNA.

Prokaryotic cells reproduce by simple cell division, a process known as _____.

binary fission

How is the total magnification of a light microscope calculated?

Magnification of the eyepiece lens multiplied by the magnification of the objective lens.

What is the formula for calculating the magnification of an image?

Magnification = size of image / real size of object.

What are two key advantages of electron microscopes over light microscopes?

They have a much higher magnification and a better resolving power (resolution).

Define 'resolution' in the context of microscopy.

The shortest distance between two points on an object that can still be distinguished as two separate entities.

The process by which an unspecialised cell becomes a more specialised cell type is called _____.

differentiation

How are sperm cells adapted for fertilisation?

They have a long tail for swimming, a streamlined head, many mitochondria for energy, and enzymes to digest through the egg's outer layer.

What is the function of the long axon in a nerve cell?

To carry electrical impulses from one part of the body to another.

How are muscle cells adapted for contraction?

They contain protein fibres that can slide over each other and have many mitochondria to provide energy for contraction.

How is a root hair cell adapted for absorbing water and mineral ions?

It has a large surface area and a thin wall to maximise absorption from the soil.

What is the function of xylem cells in a plant?

To transport water and mineral ions from the roots to the leaves, and to provide support.

How are xylem vessels adapted to form a continuous column for water transport?

The end walls between cells break down, and the cells die, becoming hollow tubes strengthened by lignin.

What is the function of phloem cells in a plant?

To transport dissolved sugars (food) up and down the plant.

What structures in phloem allow dissolved sugars to pass through the end walls of the cells?

Sieve plates, which are pores in the end walls.

What is the role of the companion cell in phloem tissue?

It provides energy from its mitochondria to the phloem vessel cell for the transport of substances.

What is a gene?

A section of a DNA molecule that codes for a specific protein.

Human body cells normally have 46 chromosomes, arranged in _____ pairs.

23

What are the two main stages of the cell cycle before the cell divides?

Growth and DNA replication, followed by mitosis.

What happens during mitosis?

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

What is the end result of the cell cycle (including mitosis and cytokinesis)?

Two new cells that are genetically identical to the original cell.

Why is mitosis important for multicellular organisms?

It is essential for growth and for replacing worn out or damaged cells.

What is a stem cell?

An undifferentiated cell that can divide to produce more stem cells and can differentiate into various specialised cells.

Where are embryonic stem cells found and what is their key capability?

They are found in an early-stage embryo and can differentiate into any type of cell in the body.

Where are adult stem cells primarily found in humans, and what is their main limitation?

They are found in tissues like bone marrow and can only differentiate into a limited range of cell types, such as blood cells.

In plants, unspecialised stem cells are found in regions called _____.

meristems

What is therapeutic cloning?

A process where an embryo is produced with the same genes as the patient to provide perfectly matched embryonic stem cells for treatment.

Give two medical conditions that scientists hope to treat using stem cells.

Type 1 diabetes and paralysis caused by spinal cord injury.

What is a major risk associated with using stem cells from a donor in medical treatments?

The patient's immune system may reject the cells because they are identified as foreign.

What is a common ethical objection to the use of embryonic stem cells in research?

Some people believe it is wrong because it involves the destruction of a potential human life.

Define diffusion.

The net movement of particles from an area of higher concentration to an area of lower concentration.

The difference in concentration between two areas is known as the _____.

concentration gradient

Name three factors that increase the rate of diffusion.

A larger concentration gradient, a higher temperature, and a greater surface area.

Why do large multicellular organisms need specialised exchange surfaces like lungs?

They have a small surface area to volume ratio, so diffusion across their outer surface is insufficient to meet their metabolic needs.

Define osmosis.

The diffusion of water molecules from a dilute solution to a more concentrated solution through a partially permeable membrane.

What happens to an animal cell when placed in pure water?

It will take in water by osmosis and burst, as it has no cell wall.

What happens to a plant cell when placed in pure water?

It takes in water by osmosis, swells, and becomes firm or 'turgid', but does not burst due to the cell wall.

What happens to a plant cell when placed in a concentrated sugar solution?

It loses water by osmosis, the cell contents shrink and pull away from the cell wall, and the cell becomes 'flaccid' or 'plasmolysed'.

Define active transport.

The movement of substances from a more dilute solution to a more concentrated solution (against a concentration gradient), which requires energy from respiration.

How do plant root hairs absorb mineral ions from the soil when the ion concentration in the soil is low?

They use active transport, which requires energy to move the ions against the concentration gradient.

Why do root hair cells contain many mitochondria?

To provide the energy from respiration needed for the active transport of mineral ions.

How is glucose absorbed from the gut into the blood when the concentration in the gut is lower than in the blood?

By active transport, moving the glucose against its concentration gradient.

Write the number 120,000,000 in standard form.

1.2 × 10⁸

Write the number 0.000007 in standard form.

7 × 10^-6

What does one order of magnitude represent?

A factor of 10 times.

A dog is 100 times longer than a woodlouse. How many orders of magnitude larger is the dog?

Two orders of magnitude larger.

A bacterium divides by binary fission every 20 minutes. How many bacteria will there be after 2 hours, starting with one bacterium?

64 bacteria (2 hours = 120 minutes; 120/20 = 6 divisions; 2⁶ = 64).

What is the formula for calculating the number of bacteria in a population after a certain time?

Number of bacteria = (initial number of bacteria) × 2ⁿ, where 'n' is the number of divisions.

In the required practical investigating osmosis in potato tissue, what is the independent variable?

The concentration of the sucrose (or salt) solution.

In the osmosis practical, what is the dependent variable?

The percentage change in mass of the potato cylinders.

How do you calculate the percentage change in mass for the osmosis practical?

% change = ((final mass - initial mass) / initial mass) × 100

In the osmosis practical, what does it mean if the potato cylinder's mass increases?

The external solution was more dilute (had a higher water potential) than the potato cells, so water moved into the potato by osmosis.

In the graph for the osmosis practical, the point where the line of best fit crosses the x-axis represents what?

The concentration of the solution that is isotonic to the potato cells, where there is no net movement of water.

What is the purpose of sterilising the petri dish and agar before culturing microorganisms?

To kill any unwanted microorganisms that could contaminate the culture.

Why must an inoculating loop be sterilised by passing it through a flame before use?

To kill any bacteria present on the loop, ensuring only the desired microorganism is transferred.

Why are agar plates incubated at 25°C in a school laboratory?

To reduce the risk of growing pathogens that are harmful to humans, which grow best at body temperature (around 37°C).

Why is the lid of a petri dish taped on but not sealed completely when culturing bacteria?

To prevent airborne microorganisms from contaminating the culture while still allowing oxygen to enter for aerobic respiration.

In the required practical investigating antibiotics, what is the 'zone of inhibition'?

The clear area around an antibiotic disc where bacteria have been killed or their growth has been prevented.

How can you compare the effectiveness of different antibiotics using the zone of inhibition?

A larger zone of inhibition indicates a more effective antibiotic against that particular bacterium.

What is the formula to calculate the area of the zone of inhibition?

Area = πr² , where 'r' is the radius of the circular zone.

In the antibiotic practical, what is used as a control?

A sterile paper disc soaked in sterile water, which should show no zone of inhibition.

When using a light microscope, which objective lens should you start with?

The lowest power objective lens.

Which focusing dial should be used first with the low-power objective lens to find the specimen?

The coarse focusing dial.

Which focusing dial is used to get a clear, sharp image, especially with high-power objective lenses?

The fine focusing dial.

What is the term for cloning plants to produce identical offspring quickly and economically?

Tissue culture (or micropropagation).

The process of cloning is useful for preserving rare plant species and for producing large numbers of crop plants with desirable features like _____.

disease resistance

What term describes the female sex chromosomes in humans?

XX

What term describes the male sex chromosomes in humans?

XY

In bacterial cells, genes that provide genetic advantages, such as antibiotic resistance, are often carried on _____.

plasmids

A typical human cell is approximately 10-20 ____ in size.

micrometres (μm)

A solution that has a higher concentration of solutes than a cell is described as _____.

hypertonic

A solution that has a lower concentration of solutes than a cell is described as _____.

hypotonic

A solution that has the same concentration of solutes as a cell is described as _____.

isotonic

The pressure exerted on the cell wall by the swollen contents of a plant cell is known as _____ pressure.

turgor

What are 'aseptic techniques' in the context of microbiology?

Procedures used to prevent contamination of cultures by unwanted microorganisms.

A student observes a bacterial cell using a microscope with an eyepiece lens magnification of ×10 and an objective lens of ×40. The image size of the bacterium is measured as 2 mm. Given that the typical size of a prokaryotic cell is 0.2 µm – 2.0 µm, which calculation correctly determines the actual size of this bacterium and confirms it is within the expected range?

Actual size = 2 mm / (10 × 40) = 0.005 mm = 5 μm. This is likely the image of a bacterial colony, not a single cell.

In the required practical investigating osmosis, a potato cylinder with an initial mass of 2.50 g is placed in a concentrated sucrose solution. After 24 hours, its mass is 2.15 g. What is the percentage change in mass?

-14%

A bacterial culture starts with 500 cells. If the bacteria divide by binary fission every 30 minutes, how many cells will there be after 4 hours, and what is this number in standard form (to two decimal places)?

128000 cells; 1.28 × 10⁵

A scientist measures the zone of inhibition around an antibiotic disc on an agar plate. The diameter of the clear zone is 18 mm. What is the area of this zone?

254.47 mm

Which of the following correctly describes why therapeutic cloning could be more advantageous for a patient needing a stem cell transplant compared to using cells from a donor?

The patient’s immune system is less likely to reject the cells because they are genetically identical.

A plant cell is placed in a solution and becomes 'flaccid'. What does this indicate about the relative water potential of the cell's cytoplasm and the external solution?

The external solution was hypertonic, causing a net movement of water out of the cell.

Why can single-celled organisms like an amoeba rely on diffusion for gas exchange, whereas multicellular organisms like humans cannot?

Single-celled organisms have a large surface area to volume ratio, allowing for efficient diffusion across their entire surface.

Which of the following comparisons between a light microscope and a transmission electron microscope (TEM) is correct?

Light microscopes can be used to view living specimens, while TEMs require thin, dead sections of the specimen.

Which statement accurately describes a key feature of binary fission in prokaryotic cells?

The circular DNA and plasmids replicate, and the cell divides into two genetically identical daughter cells.

A sperm cell is highly specialised for its function. Which of these is NOT an adaptation of a sperm cell?

A full set of 46 chromosomes to ensure the zygote is diploid.

A cell from a plant's leaf and a cell from its root are examined. Which subcellular structure would be abundant in the leaf cell but absent in the root hair cell?

Chloroplasts

Which process moves glucose from the gut into the blood when the concentration of glucose in the blood is already higher than in the gut?

Active Transport

A typical human cell is approximately 10-20 micrometres (µm) in size, and a typical bacterial cell is 0.2-2.0 µm. How many orders of magnitude larger is a human cell than a bacterial cell?

One order of magnitude

Which of these correctly identifies a key difference between eukaryotic and prokaryotic cells?

Eukaryotic cells divide by mitosis, whereas prokaryotic cells divide by binary fission.

A student is asked to write the diameter of a red blood cell, 7 µm, in metres using standard form. Which is the correct representation?

7 × 10^-6 m