Biology 2.1.1 Cell structure

Question 1

Describe how a light microscope works

Answer 1

Eyepiece and objective lenses produce a magnified image of a specimen
The specimen sample is illuminated by light

Produces 2D coloured images
Living samples

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

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

Question 3

Outline how a wet mount microscope slide is prepared for use in light microscopy

Answer 3

1. The specimen must be thin
2. Place specimen at centre of the slide in a drop of water
   3.Cover slip must be placed at an angle over the specimen to avoid air bubbles

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 sacs enclosed by membranes

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 mitochodrial DNA

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 a membranous sac
Lysosomes contain hydrolytic enzymes which breakdown waste material in the cell

Question 23

Outline the structure and function of cilia and flagella

Answer 23

Cilia is hair-like structures that protrude from cell

Cilia beat and waft away substances

Flagella is whip-like structures that protrude from cell

Flagella enable cell mobility

Cilia anad flagella contain microfilaments which enable cell movement

Question 24

Outline the structure and function of the cell wall

Plant, bacterial and fungal

Answer 24

Plant - Cellulose
Bacterial - Peptidoglycan
Fungal - Chitin

The cell wall provides structure and support to the cell

Question 25

Outline the structure and function of centrioles

the cytoskeleton, centrosomes and cell division

Answer 25

Centrioles are a component of the cytoskeleton, composed of microtubules

Centrioles form centrosomes

Centrosomes migrate to opposite poles of cell and spindle fibres form between them during cell division

an example of microtubules in the cytoskeleton aiding transport in cell

Question 26

Describe the structure and function of the cytoskeleton

Functions of microfilaments, microtubules and intermediate fibres

Answer 26

Microfilaments enable cell movement
Microtubules aid transport within the cell
Intermediate fibres provide mechanical strength to the cell

Question 27

Contrast eukaryotic cells and prokaryotic cells

Prokaryotes

Answer 27

Prokaryotes

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

Question 28

Contrast eukaryotic cells and prokaryotic cells

Eukaryotes

Answer 28

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

Question 29

Outline the function of organelles involved in protein production

Nucleus, Rough endoplasmic reticulum, golgi apparatus, vesiscles

Answer 29

Nucleus - DNA molecules code for specific proteins
RER - Site of protein synthesis
Golgi apparatus - Proteins modified and packaged
Vesicles - Transportation of proteins out of or around the cell