Cell Biology

Why must microorganisms be cultured in sterile conditions?

To prevent contamination from unwanted microbes that may compete or mutate into pathogens.

How do you sterilise an inoculating loop?

By passing it through a flame.

Why should you only partially seal and store a Petri dish upside down?

To allow oxygen in and prevent condensation from contaminating the culture.

Why is 25°C used for incubating school cultures?

To avoid growing harmful bacteria that prefer body temperature (37°C).

How do bacteria reproduce?

By binary fission.

How often can bacteria divide in ideal conditions?

About every 20 minutes.

What is the formula for calculating bacterial population?

Final population = starting number × 2^(number of divisions).

How are antibiotics tested on bacteria?

Using antibiotic-soaked discs on an agar plate with bacteria.

What does a clear zone around an antibiotic disc show?

That the antibiotic killed or inhibited bacterial growth.

How do you measure the effectiveness of an antibiotic?

By calculating the area of the inhibition zone using πr².

What are chromosomes and how many do humans have?

Structures made of DNA that carry genetic information; humans have 46 chromosomes.

What is a gene?

A segment of DNA that codes for a specific protein or characteristic.

What is the purpose of mitosis?

To produce two identical daughter cells for growth and repair.

What are stem cells?

Undifferentiated cells that can become different cell types.

Where are stem cells found?

In embryos, adult bone marrow, and plant meristems.

What is therapeutic cloning and its benefit?

Creating an embryo with the patient's DNA to produce stem cells that won't be rejected.

What are advantages and disadvantages of stem cell use?

Advantages: treat disease, repair tissues; Disadvantages: ethical issues, risk of infection, high cost.

What is diffusion?

The movement of particles from high to low concentration.

What factors affect the rate of diffusion?

Concentration difference, temperature, and surface area.

Why do large organisms need exchange surfaces?

They have low surface area to volume ratios and can't rely on diffusion alone.

How are lungs and intestines adapted for efficient diffusion?

They have large surface areas, thin walls, and rich blood supplies.

What is osmosis?

The movement of water from a dilute to a concentrated solution through a semi-permeable membrane.

How do plant and animal cells react in hypertonic or hypotonic solutions?

Animal cells burst or shrink; plant cells become turgid or plasmolysed.

What does a mass change in potato osmosis experiments indicate?

Gain shows water entered (hypotonic), loss shows water left (hypertonic).

What structures are found in all eukaryotic cells?

Cell membrane, cytoplasm, nucleus containing DNA.

What type of cells are bacteria?

Prokaryotic.

What structures do bacterial cells have?

Cell wall, cell membrane, cytoplasm, single circular DNA strand, plasmids.

What are organelles?

Structures within cells that perform specific functions.

What is the difference in DNA location between eukaryotic and prokaryotic cells?

Eukaryotic DNA is in the nucleus; prokaryotic DNA floats freely in the cytoplasm.

What are plasmids?

Small rings of DNA in bacterial cells.

What do the prefixes centi-

milli-, micro-, and nano- mean?,Centi: ×0.01, Milli: ×0.001, Micro: ×0.000001, Nano: ×0.000000001.

What does it mean if something is 10³ times bigger?

It is 1000 times bigger.

What is the function of the nucleus?

Contains DNA and controls cell activities.

What is the function of the cytoplasm?

Site of chemical reactions; contains enzymes and organelles.

What is the function of the cell membrane?

Controls what enters and exits the cell.

What happens in mitochondria?

Aerobic respiration to release energy.

What is the role of ribosomes?

Site of protein synthesis.

What is the function of chloroplasts?

Site of photosynthesis; contains chlorophyll.

What is the function of the permanent vacuole?

Maintains cell rigidity; contains cell sap.

What is the plant cell wall made of and what is its function?

Cellulose; provides strength and structure.

What is the bacterial cell wall made of?

Peptidoglycan.

What is cell specialisation?

When cells develop specific features for a particular function.

What is differentiation?

The process by which cells become specialised.

Do animal and plant cells both differentiate?

Animals: mostly only during development; Plants: throughout life.

How do stem cells work?

They differentiate by switching specific genes on or off.

How are sperm cells adapted for their function?

Streamlined head, tail for movement, many mitochondria, enzymes in acrosome.

How are nerve cells adapted for quick signal transmission?

Long axons, dendrites, mitochondria in synapses.

How are muscle cells adapted for contraction?

Protein filaments, mitochondria, glycogen stores.

How are root hair cells adapted for absorption?

Large surface area, vacuole, mitochondria for active transport.

How are xylem cells adapted for water transport?

Lignin walls, hollow tubes, end-to-end structure.

How are phloem cells adapted for food transport?

Sieve plates, companion cells with mitochondria.

How are red blood cells replaced?

By adult stem cells as they can't divide themselves.

Why does cell division occur in mature animals?

For repair and replacement of damaged cells.

When can plant cells re-differentiate?

When moved to a new position in the plant.

What do microscopes do?

Magnify small structures like cells.

How does a light microscope work?

Uses lenses to focus light and magnify images.

What is the max magnification and resolution of a light microscope?

~x2000 magnification, 200nm resolution.

What can be seen with a light microscope?

Tissues, cells, large sub-cellular structures.

What does an electron microscope use?

Electrons to form higher-resolution images.

What are the two types of electron microscopes?

Scanning (SEM) and Transmission (TEM).

What are the magnifications and resolutions of SEM and TEM?

SEM: x2,000,000, 10nm; TEM: x2,000,000, 0.2nm.

How do you calculate magnification?

Eyepiece lens × Objective lens.

How do you calculate object size?

Image size ÷ Magnification.

What is standard form and why is it useful?

A way of expressing large or small numbers; helps in scientific calculations.

Give an example of standard form.

1.5 × 10⁻⁵ = 0.000015.

Why are microorganisms cultured?

To grow large numbers for study.

What does a culture medium contain?

Carbohydrates, minerals, proteins, vitamins.

What are two main methods for culturing microorganisms?

Nutrient broth and agar gel plates.

How is a nutrient broth culture made?

Mix bacteria in sterile broth, stopper with cotton wool, shake for oxygen.

How are agar plates prepared?

Pour sterile agar into Petri dish, cool, inoculate, tape lid, incubate upside down.

Why must culture equipment be sterilised?

To prevent contamination by other microbes.

How are Petri dishes sterilised?

Using an autoclave or UV light.

Why are agar plates stored upside down?

To stop condensation from dripping onto the agar.