Biology 2.1.1 Cell structure

Question 1

Describe how a light microscope works

Answer 1

Light is transmitted through thin layer of a specimen supported on a glass slide
The light is focused through the eyepiece leans and objective lens to produce a magnified image

Produces 2D coloured images
Living samples
Resolution (200nm) and magnification (1500x) are low
Cheap and fast

Question 1

Describe how a transmission electron microscope works

Answer 1

A beam of electrons is passed through a specimen
The beam of electrons is focused to produce a magnified image

Produces 2D black and white images
Non-living samples
Resolution (0.2nm) and magnification (500,000x) are high
Expensive and requires training

Question 2

Describe how a scanning electron microscope works

Answer 2

A beam of electrons is reflected across the surface of the specimen
The reflections are collected to produce a magnified image

Produces 3D black and white images
Non-living specimens
Resolution (10nm) and magnification (100,000x) are high
Expensive and requires training

Question 3

State dry mount slide preparation of a solid specimen

Answer 3

Solid specimen is cut into thin slices
The specimen is placed on the centre of the slide
Apply a stain to the specimen
The cover slip is placed over the sample using a scalpel or forceps

Question 4

Explain why staining is used in light microscopy

Answer 4

Differential staining: The increase contrast allows the components to become distinguished and identified

Question 5

Outline how a light microscopic image must be drawn and annotated

Answer 5

Use sharp pencil, no shading, smooth lines
State title, scale bar, magnification
Label lines must not cross or have arrowheads Label lines must be drawn with a ruler
Drawing must take up at least half the page

Question 6

State the magnification formula

Answer 6

Magnification = size of image/actual size of object

Question 7

Define magnification and resolution

Answer 7

Magnification - factor by which the image is larger than the actual specimen
Resolution - The ability to distiguish between two structures

Question 8

Describe the relative differences in magnication and resolution between light microscopy, TEM and SEM.

Learners are not required to recall exact resolutions or magnification

Answer 8

Light microscopy - low magnification and resolution
TEM and SEM - high magnifictaion and resolutiton

Question 9

Explain the calibration and use of the eyepiece graticule and stage micrometer in light microscopy

Answer 9

1. Line up stage micrometer and eyepiece graticule
2. Count how many divisions on the eyepiece graticule are in one division of the micrometer
3. Each division on the micrometer is 10μm. Calculate the length of one division on the eyepiece graticule
4. The calibration can be used to measure the actual size of an object in light microscopy

Question 10

Describe the structure of the nucleus

Outline functions of Nuclear envelope, Nuclear pores and Nucleolus

Answer 10

Nuclear envelope - double membrane which surrounds the nucleus
Nuclear pores - allow substances in and out of the nucleus
Nucleolus - within the nucleus and contains proteins and RNA that assemble ribosomes

Question 11

Outline the function of the nucleus

Outline the function of DNA molecules within the cell

Answer 11

The nucleus contains DNA molecules
DNA directs the synthesis of proteins within the cell
DNA controls the metabolic activities within the cell

Question 12

Describe the structure of the endoplasmic reticulum

Rough and smooth

Answer 12

A compact structure made up of cisternae

Cisternae - Network of flattened membrane-bound sacs

Question 13

Outline the function of the endoplasmic reticulum

Rough and smooth

Answer 13

Rough - synthesis and transport of proteins

Smooth - synthesis of lipids and carbohydrates

Question 14

Describe the structure of the golgi apparatus

Answer 14

A compact structure made up of cisternae

Cisternae - Network of flattened sacs enclosed by membranes

Question 15

Outline the function of the golgi apparatus

Answer 15

Modifies proteins
Packages proteins into vesicles

Question 16

Describe the structure of ribosomes

Answer 16

Ribosomes are non-membrane bound organelles made up of RNA molecules made in the nucleolus of the cell

Question 17

Outline the function of ribosomes

Answer 17

Protein synthesis

Question 18

Describe the structure of mitochondria

Outline the name and function of the inner membrane and fluid interior

Answer 18

The mitochondria consists of a double membrane

Folded inner membrane called cristae, containing enzymes for aerobic respiration

Fluid interior called the matrix, containing mitochondrial DNA (so mitochondria can produce their own enzymes and reproduce themselves)

Question 19

Outline the function of the mitochondria

Answer 19

Mitochondria is the site of aerobic respiration to produce ATP

Question 20

Describe the structure of chloroplasts

Describe thykaloids, granum, lamallae and stroma

Answer 20

Chloroplasts consist of a double membrane

Thykaloids - network of membranes, which forrm flattened sacs

Grana - stacks of thykaloids, containing chlorophyll

Lamallae - membranes which join granum together

Stroma - fluid interior, containing chloroplast DNA

Question 21

Outline the function of chloroplasts

Answer 21

Site of photosynthesis

Question 22

Describe structure and function of lysosomes

Answer 22

Lysosomes are specialised vesicles
Lysosomes contain hydrolytic enzymes which breakdown waste material in the cell

Question 23

Outline the structure and function of the cell wall

Plant, bacterial and fungal

Answer 23

Plant - Cellulose
Bacterial - Peptidoglycan
Fungal - Chitin

The cell wall provides structure and support to the cell

Question 24

Contrast eukaryotic cells and prokaryotic cells

Prokaryotes

Answer 24

Prokaryotes

• small, make up unicellular organisms
• no membrane bound organelles, no nucleus
• unassociated circular DNA
• small ribosomes (70s)
• peptidoglycan cell wall

Question 25

Contrast eukaryotic cells and prokaryotic cells

Eukaryotes

Answer 25

Eukaryotes
* large, make up multicellular organisms
* membrane bound organelles, contains nucleus
* associated linear DNA
* large ribosomes (80s)
* cellulose/chitin cell wall

Question 26

Outline the function of organelles involved in protein production and secretion

Answer 26

Nucleus - DNA molecules code for specific proteins
RER - Site of protein synthesis
Golgi apparatus - Proteins modified and packaged
Vesicles - Transportation of proteins around the cell along the cytoskeleton
Plasma membrane - Secretory vesicles fuse to membrane for secretion by exocytosis of proteins

Question 27

Describe the structure and function of the flagella and cilia

Answer 27

The cytoskeleton enables cell movement via cilia and flagella
These structures are both hair-like extensions that protrude from the cell surface and contain microtubules that are responsible for moving them as they contract

Question 28

Describe the stucture and function of centrioles

Answer 28

Centrioles are made up of microtubules. Centrioles consist of small, hollow cylindrical proteins called microtubules.
Centrioles help chromosomes separate during cell division.
Centrosomes migrate to oppoite sides of poles and produce spindle fibres to separate chromosomes

Question 29

Outline the functions of the microfilaments of the cytoskeleton

Answer 29

Microfilaments - solid strands that are mostly made of the protein actin.
Microfilaments aid in cellular movement and cell contraction.

Question 30

Outline the function of microtubules in the cytoskeleton

Answer 30

Microtubules are tubular (hollow) strands that are mostly made of the protein tubulin. Organelles and other cell contents are moved along these fibres.

Microtubules aid in intracellular movement by forming ‘tracks’ along which organelles can move e.g. vesicles through the cell, chromosomes along spindle fibres.

Question 31

Outline the function of intermediate fibres in the cytoskselton

Answer 31

Intermediate fibres provides the cell with mechanical strength, forming a kind of ‘scaffolding’ that helps to maintain the shape of the cell.
It also supports the organelles, keeping them in position.

Question 32

Outline the general importance of the cytoskeleton within the cell

Answer 32

• Mechanical strength of the cell
• Transport within the cell
• Cell movement

Question 33

Describe how a laser scanning confocal microscope works

Answer 33

A specimen is treated with a fluorescent dye
Fluorescence is the absorption and re-radiation of light
A single spot of focused light (laser) moves across a specimen
The light is re-radiated by fluorescent components of the specimen
The re-radiated light is focused through a narrow pin-hole and detected to produce a magnified image

Can produce 2D images or 3D images by creating images from different planes
Produces coloured images
High resolution as the narrow pinhole blocks out any re-radiated light that is out of focus

Question 34

Why may a wet mount be used for a microscopic slide

Answer 34

To prevent dehydration of a specimen

Question 35

Why is it important for a specimen to be thin for a light microscopic slides and what are the methods for achieving this?

Answer 35

To allow individual cells to be seen
To allow maximum light to penetrate the tissue
Using a sharp blade to ensure the specimen is thin
Selected the thinnest slides for observation

Question 36

Why must a cover slip be placed at an angle over a specimen when preparing a microscopic slide?

Answer 36

To prevent the formation of air bubbles