Topic 1.1: Cell Structure

What are the main characteristics of a eukaryotic organism?

A eukaryotic organism is an organism whose cells contain membrane-bound organelles, e.g. a nucleus and mitochondria.

True or False? Prokaryotic organisms contain a nucleus.

False
Prokaryotic organisms do not contain a nucleus.

What is a prokaryotic organism?

A prokaryotic organism is an organism whose cells lack a nucleus and other membrane-bound organelles.

True or False? All prokaryotic organisms are single-celled.

True
Prokaryotic organisms are always single-celled.

Define the term plasmid.

A plasmid is a small circular loop of DNA found in prokaryotic cells.

True or False? Eukaryotic cells are larger than prokaryotic cells.

True

• Eukaryotic cells: 10–100 µm
• Prokaryotic cells: ~1 µm
  Eukaryotic cells are larger than prokaryotic cells.

How many micrometres (µm) are in a millimetre (mm)?

There are 1000 µm in 1 mm.
There are 1,000,000 nanometres in a millimetre.

What is 1,000,000 in standard form?

1,000,000 in standard form is 1 × 10⁶.

True or False? To convert a measurement from nanometres to micrometres you must multiply by 1000.

False
To convert from nanometres to micrometres, you must divide by 1000.

If a eukaryotic cell is 100 µm wide and a prokaryotic cell is 1 µm wide, how much bigger is the eukaryotic cell in terms of orders of magnitude?

The eukaryotic cell is 2 orders of magnitude wider.
1 = 10⁰ and 100 = 10², therefore the difference is 2 orders of magnitude.

What separates cells from their surrounding environment?

The cell membrane separates cells from their surrounding environment.

Name the largest organelle present within animal cells.

The nucleus is the largest organelle within animal cells.

Name the structures present in plant cells that are not present in animal cells.

Plant cells have:

• Cell wall
• Chloroplasts
• Permanent vacuole

True or False? Ribosomes are present in both plant and animal cells.

True
Ribosomes are present in both and are the site of protein synthesis.

Name three organelles found within animal cells.

Examples:

• Nucleus
• Mitochondria
• Ribosomes

What is the smallest organelle present in both plant and animal cells?

Ribosomes are the smallest organelle, present in both plant and animal cells.

True or False? The gel-like fluid present inside both plant and animal cells is the chloroplast.

False
The gel-like fluid is the cytoplasm.
Chloroplasts are organelles found only in plant cells.

True or False? The role of the nucleus is to release energy for the cell.

False
The nucleus stores genetic information (DNA).
Energy is released by the mitochondria.

What is the function of chloroplasts within plant cells?

Chloroplasts absorb light energy during photosynthesis.

True or False? Plant cell walls are responsible for controlling the passage of substances in and out of cells.

False
The cell wall provides strength and structural support.
The cell membrane regulates passage of substances.

What is the function of the permanent vacuole in plant cells?

The permanent vacuole stores cell sap and provides structural support.

True or False? Mitochondria are the site of aerobic respiration.

True
Mitochondria release energy via aerobic respiration.

Define the term specialised cell.

Specialised cells are cells that develop specific characteristics to perform particular functions.

Give an example of a specialised plant cell.

Examples:

• Root hair cell
• Palisade mesophyll cell
• Xylem cell
• Phloem cell

Give an example of a specialised animal cell.

Examples:

• Red blood cell
• Nerve cell
• Ciliated epithelial cell
• Sperm cell / Egg cell
• Muscle cell
  (You need to know sperm, nerve, and muscle cells specifically.)

True or False? Root hair cells have an increased surface area.

True
Root hair cells have an increased surface area to absorb water and minerals.

What is the function of a nerve cell?

Nerve cells conduct electrical impulses and send signals around the body.

True or False? An adaptation of a muscle cell is that they contain a lot of mitochondria.

True
Muscle cells contain many mitochondria for aerobic respiration and muscle contraction.

True or False? Sperm cells contain a full set of chromosomes (46) from the father.

False
Sperm cells contain half the DNA of normal body cells (haploid).

Why are root hair cells adapted to contain a large number of mitochondria?

They contain many mitochondria to provide energy for active transport of mineral ions.

What is the function of a phloem cell?

Phloem cells form long vessels to transport dissolved sugars and amino acids.

True or False? Phloem vessels are strengthened and supported by lignin.

False
It is xylem vessels that are supported by lignin.

What is cell differentiation?

Cell differentiation is the process where a cell changes to become specialised.

True or False? Almost all cells in a multicellular organism contain different genetic information.

False
Almost all cells contain the same genetic information.

What determines the features of specialised cells?

The expression of genes in the nucleus determines specialised cell features.

True or False? All plant cells differentiate early in development.

False
Many plant cells retain the ability to differentiate throughout life.

When does most cell differentiation occur in animals?

During early development (embryo/fetus stage, before birth).

What is a light microscope?

An instrument using light and lenses to magnify specimens and view cells or large subcellular structures.

What does resolution mean in microscopy?

The ability to distinguish two close objects as separate entities.

What is an electron microscope?

An instrument that uses electron beams instead of light, providing higher resolution and magnification.

True or False? Electron microscopes use light beams for imaging.

False
Electron microscopes use electron beams.

True or False? Upon invention of the light microscope in the 17th century, scientists could view cell structure in detail.

False
Early light microscopes showed only basic details like shape and cell walls.

What is the formula for calculating magnification?

Magnification = image size ÷ actual size

True or False? Magnification has units.

False
Magnification has no units (e.g. ×10, 5000×).

What is the equation for calculating the actual size of a specimen?

Actual size = image size ÷ magnification

What is the purpose of a magnification scale in microscope drawings?

It shows the actual size of the specimen.

What is a microscope slide?

A thin flat piece of glass on which specimens are prepared for observation.

What stain is used for cheek cells?

Methylene blue

True or False? Iodine is used to stain onion cells.

True
Iodine stains onion cells.

What should be avoided when preparing a microscope slide?

Avoid:

• Smudging the slide
• Trapping air bubbles under the coverslip

What is an objective lens?

The lens closest to the specimen.
Most microscopes have multiple objective lenses of different powers.

True or False? The highest-powered objective lens should always be used first.

False
Always start with the low-power lens first.

What are the key characteristics of biological drawings?

Rules for biological drawings:

• Use a sharp pencil
• Lines must be clear and unbroken
• Draw proportionally
• Use straight, uncrossed labels

How large should biological drawings be?

They should take up at least half of the page.

Define the term binary fission.

Binary fission is a simple type of cell division used by bacteria to multiply.

What happens to the number of bacterial cells after binary fission?

The number of cells doubles (increases by a power of 2) each time.

What is aseptic technique?

A method to prevent contamination by unwanted microorganisms when working with cultures.

True or False? Lifting the lid of a petri dish only slightly prevents air from entering.

False
It reduces contamination by other microorganisms.

Why should the inoculating loop be passed through a hot flame before use?

To sterilise it by killing microorganisms, preventing contamination.

Why should the lid of the petri dish be taped at intervals, not sealed all the way around?

So oxygen can enter, preventing growth of harmful anaerobic bacteria.

What is the highest incubation temperature for growing bacteria in a school lab and why?

Maximum: 25°C
This limits growth of harmful pathogens.

What is an inhibition zone?

An area around an antibiotic/antiseptic disc where bacterial growth is inhibited.

What is the equation for calculating the area of an inhibition zone?

Area = πr²
(π = 3.14, r = radius of the inhibition zone)

What is the mean division time of bacteria?

The average time for a bacterial cell to divide.

True or False? A large zone of inhibition indicates the antibiotic is effective.

True
The larger the zone, the more effective the antibiotic.

What is indicated by the absence of a zone of inhibition around an antibiotic disc?

The bacteria are resistant to that antibiotic.

When investigating antibiotics on bacterial growth, what should be used as a control?

Sterile water-soaked paper discs (control group).

How can microorganisms be cultured for investigation?

They can be grown in:

• Nutrient broth solution

• Agar gel plat