2.1.1 Cell structure

Question 1

What is magnification?

Answer 1

Magnification is how many times larger an image is than the actual object.

Question 2

What is resolution?

Answer 2

Resolution is the ability to distinguish between two separate points
It determines how detailed an image is.

Question 3

What is the formula for calculating magnification?

Answer 3

-

Question 4

What is an eyepiece graticule used for?

Answer 4

A scale fitted into the eyepiece used to measure objects under the microscope, but it must be calibrated for accuracy.

Question 5

What is a stage micrometer used for?

Answer 5

A slide placed on the stage with a known scale (in µm) used to calibrate the eyepiece graticule.

Question 6

How do you calculate the size of one graticule division?

Answer 6

Graticuledivision= Numberofgraticuledivisions ÷
Sizeofonemicrometerdivision

Question 7

If 40 graticule divisions = 1 micrometer division (10 µm), what is the size of one graticule division?

Answer 7

0.25 μm

Question 8

Name four types of microscopes.

Answer 8

• Light microscope
• Transmission electron microscope (TEM)
• Scanning electron microscope (SEM)
• Laser scanning confocal microscopes

Question 9

What are the resolution and magnification limits of a light microscope?

Answer 9

Resolution: ~0.2 µm

Magnification: up to x1,500

Question 10

What are four slide preparation techniques?

Answer 10

• Wet mounts
• Dry mounts - Specimen is placed directly onto slide and covered with a cover slip.
• Squash slides - A wet mount is prepared and the cover slip is pressed to squash the cells.
• Smear slides - Edge of a slight is used to smear the sample to create a thin, even coating on a seperate slide.

Question 11

What are the steps for preparing a wet mount slide?

Answer 11

1. Use a pipette to place a small drop of water onto the centre of the glass slide.
2. Use a pair of forceps to place a thin section of the live specimen onto the drop of water. The specimen should be thin enough to allow light to pass through it.
3. Add a few drops of stain to the specimen - increases contrast & allows cell components to become visible.
4. Slowly add a cover slip onto the specimen

Viola✨

Question 12

Why is differential staining used?

Answer 12

It uses multiple stains to distinguish between different cells or organelles.

Question 13

What are the basic steps to view a slide under a light microscope?

Answer 13

1. Clip the prepared microscope slide onto the stage.
2. Select objective lens with lowest power
3. Use coarse focus to bring stage up.
4. Look through eyepiece and slowly lower stage to focus, using coarse focus.
5. Use fine focus for a clear image.
6. ncrease magnification if needed and refocus.

Question 14

What are the key features of a good biological drawing?

Answer 14

Include a title
State magnifications or scale
Be drawn with a sharp pencil
Include smooth, continuous lines
Include labels
Include accurate sizes of observable features
No shading ot colouring
No arrow heads
Lines cannot overlap each other.

Question 15

How does an electron microscope differ from a light microscope?

Answer 15

It uses a beam of electrons (instead of light) to form an image, providing much higher resolution and magnification.

Question 16

What are the advantages and disadvantages of electron microscopes?

Answer 16

✅ Higher resolution and magnification
❌ Expensive
❌ Only black and white images
❌ Complex sample preparation
❌ Can only be used on dead specimens

Question 17

What are the two types of electron microscopes?

Answer 17

1. Transmission electron microscope (TEM)
2. Scanning electron microscope (SEM)

Question 18

What are the resolution and magnification limits of a TEM?

Answer 18

Resolution: ~0.5 nm

Magnification: up to ×1,500,000

Question 19

How does an SEM work and what does it show?

Answer 19

It scans electrons across the specimen’s surface.
Reflected electrons form a 3D image of the surface.

Question 20

What are the resolution and magnification limits of an SEM?

Answer 20

Resolution: ~5 nm

Magnification: up to ×1,500,000

Question 21

How do light, TEM, and SEM microscopes compare?

Answer 21

Light: Mag = ×1,500 & Res = 0.2 µm, inexpensive, 2D image, colour, specimen can be living or dead
TEM: Mag = ×1,500,000 & Res = 0.5 nm, expensive, 2D image, B&W, specimens are dead
SEM: Mag = ×1,500,000 & Res = 5 nm, expensive, 3D image, B&W, specimens are dead.

Question 22

Describe how a laser scanning confocal microscope works.

Answer 22

• Uses a laser beam to scan across a specimen that has been treated with a fluorescent dye.
• The laser excites the dye, causing it to emit light (fluorescence).
• This produces a high-resolution, sharp 2D image — multiple images at different depths can be combined to create a 3D image.

Question 23

What are the two main types of organisms based on cell structure?

Answer 23

Eukaryotes
Prokaryotes

Question 24

What is the main difference between eukaryotic and prokaryotic cells?

Answer 24

• Eukaryotic cells are more complex, contain membrane-bound organlles, have 80s chromosomes and have their DNA in the form of chromosome within the nucleus.
• Prokaryotes contain no membrane-bound organelles (no mitochondria or chloroplasts), have 70s ribsomes and have circular naked DNA with no nucleus.

Question 25

Draw a typical animal cell.

Answer 25

Label nucleus, nucleolus, RER, SER, golgi apparatus, mitochondrion, lysosome, ribosome.

Question 26

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

Answer 26

Structure: * Contains genetic info in the form of chromosomes * Contains a structure known as nucleolus * Surrounded by nuclear envelope (double memb) containing pores. Function: * Controlling cell activities - transcription * Synthesis of ribosomes - rRNA is assembled in nucleolus * Exchange between nucleus and cytoplasm - substances can enter/leave via nucelar pores.

Question 27

What is the structure and function of the **plasma (cell-surface) membrane**?

Answer 27

Structure: * Fluid mosaic model - made up of many lipids and proteins * Found on surface of animal cells are inside cell wall of plant cell. Function: * Controls movement of substances into and out of cell - partially permeable membrane * Cell signalling - receptors detect signals from other cells. * Compartmentalisation

Question 28

What is the structure and function of **mitochondria**?

Answer 28

Structure: * Surrounded by double membrane, in which inner membrane is highly folded to form cristae. * Contain their own DNA and ribosomes * Inside is matrix - contains enzymes Function: * Site of aerobic respiration - produces ATP

Question 29

What is the structure and function of **ribosomes**?

Answer 29

Structure: - Made up of proteins and rRNA, consists of a large and small subunit. - Not surrounded by membrane - Eukaryotes contain 80s ribosomes. - Either floats in cytoplasm or is attached to RER Function: - Site of protein synthesis (translation)

Question 30

What is the structure and function of the **Golgi Apparatus**?

Answer 30

Structure: - Contains fluid-filled, membrane-bound sacs known as cristernae. - Contain smaller vesicles Function: - Process and package lipids & proteins by the cristernae - Stores and transport lipds & proteins by vesicles - Synthesise lysosomes

Question 31

What is the structure and function of the **Rough Endoplasmic Reticulum** (RER)?

Answer 31

Structure: - Contains network of membranes enclosing a fluid filled, flattened sacs known as cristernae. - Surface of cristernae is covered with ribosomes. Function: - Synthesis and transport of proteins using ribsomes on surface.

Question 32

What is the structure and function of the **Smooth Endoplasmic Reticulum** (SER)?

Answer 32

Structure: - Also contains network of membranes enclosing a fluid filled, flattened sacs known as cristernae. - Without ribosomes Function: - Synthesis, storage and transport of lipids & carbohydrates (e.g. cholesterol and steroid hormones)

Question 33

What is the structure and function of **lysosomes**?

Answer 33

Structure: - Contains hydrolytic enzymes - Surrounded by membrane (vesicle) to keep enzyme separate from cytoplasm of cell Function: - Digest pathogens using hydrolytic enzymes - Break down waste material - old organelles and cells

Question 34

What are the three components of the **cytoskeleton** and their roles?

Answer 34

* **Microfilaments** - Made from actin, involved in cell **movement** & locomotion, such as crawling and muscle contraction. * **Microtubules** - Made of tubulin, form scaffold-like structures, form **spindle fibres** for cell division, act as **tracks** for intracellular transport of vesicles & organelles. * **Intermediate filaments** - Maintain **position** of organelles, responsible for **mechanical strength** of certain tissues.

Question 35

What additional organelles are found in plant cells that are not found in animal cells?

Answer 35

Cellulose cell wall, chloroplasts and permanent vacuole

Question 36

Draw a typical plant cell.

Answer 36

Label nucleus, nucleolus, RER, SER, golgi apparatus, chlorplasts, mitochondria, vacuole, ribosomes.

Question 37

What is the structure and function of a plant **cell wall**?

Answer 37

Structure: - Made of cellulose - Contains channels (gaps) known as plasmodesmata (or plasmodesma singular). Function: - Supports the cell - Contents of the cell press against cell wall to make it rigid. - Prevents cell from bursting - Wall can withstand high osmotic pressure - Allows exchange of substances between cells - Plasmodesmata connects neighbouring cells.

Question 38

What is the structure and function of **chloroplasts**?

Answer 38

Structure: - Contains fluid-filled sacs knows as thylakoids which are stacked up to form grana. - Surrounded by a double membrane, enclosing a fluid called stroma. - Contain own DNA and ribosomes Function: - Site of photosynthesis - Light-dependent in grana and light-independent in stroma.

Question 39

What is the structure and function of a **permanent vacuole**?

Answer 39

Structure: - Contains cell sap - Solution of salts & sugars - Surrounded by selectively permeable membrane known as a **tonoplast**. Function: - Helps maintain pressure within the cell, keeps cell rigid and stops plants from wilting

Question 40

What is the structure of **algal cells**?

Answer 40

* Can be unicellular or multicellular * Contain same organelles as plant cells * Contain chloroplasta with different shapes to those found in plant cells.

Question 41

What is the structure of **fungal cells**?

Answer 41

* Can be unicellular or multicellular * Contain most of organelles found in plant cells * Do not contain chloroplasts * Contains cell walls made out of **chitin** rather than cellulose.

Question 42

What is a **prokaryote**?

Answer 42

Single-celled organisms, so consist of a single prokaryotic cell. Much smaller than eukaryotic cells & do not contain a nucleus or other membrane-bound organelles.

Question 43

What is the structure of the prokaryotic cell wall made of?

Answer 43

Murein (peptidoglycan)

Question 44

What type of **ribosomes** do prokaryotic cells contain?

Answer 44

**70S ribosomes**, which are smaller than the 80S ribosomes found in eukaryotic cells.

Question 45

How is genetic material organised in prokaryotic cells?

Answer 45

Large circular strand of DNA and some extra genes found in smaller loops known as plasmids. They are naken (without histones)

Question 46

Describe some additonal organelles in prokaryotes.

Answer 46

* **Capsule** - Extra layer around celll wall, made up of polysaccharides & protects cell from attack by antibiotics or WBC. * **Flagellum** - Long hair-like structure, attached to cell membrane, rotates to push cell through movement. * **Pili** - Short hair-like structures on cell surface, used for attaching to other cells or surfaces.

Question 47

Key differences between eukaryotic and prokaryotic cells?

Answer 47

* **Cell type**: Eukaryotes are multicellular (mostly), prokaryotes are unicellular * **Size**: Eukaryotes = 10 to 100 µm, Prokaryotes = 0.1 to 5 µm * **DNA**: Eukaryotes have linear chromosomes in a nucleus; prokaryotes have circular DNA and plasmids. * **Ribosomes**: Eukaryotes = 80S, Prokaryotes = 70S. * **Organelles**: Eukaryotes have membrane-bound organelles; prokaryotes do not. * **Cell wall**: Eukaryotic plant cells have cellulose or chitin walls; prokaryotes have murein walls.