Cell Structure

Question 1

Prokaryotic and Eukaryotic

What are the two types of cells?

Answer 1

Eukaryotic- contains a nucleus.
Prokaryotic- does not contain a nucleus and is much smaller.

Question 2

Prokaryotic and Eukaryotic

How is DNA stored in a prokaryotic cell?

Answer 2

-Plasmids
-Loops

Question 3

Animal and plant cells

List the components in both plant and animal cells and their functions.

Answer 3

-Nucleus= controls the cell’s activity and contains DNA
-Cytoplasm= site of chemical reactions
-Cell membrane= controls what enters and exits the cell
-Mitochondria= Where respiration happens
-Ribosomes= Protein synthesis

Question 4

Animal and plant cells

List the additional components in plant cells.

Answer 4

-Cell wall= Extra support
-Vacuole= Contains cell sap, keeps the cell turgid
-Chloroplasts= Photosynthesis

Question 5

Cell specialisation

What is specialisation?

Answer 5

When cells adapt to perform a specific function.

Question 6

Cell specialisation

Sperm cell specialisation.

Answer 6

Haploid nucleus- contains genetic information.
Tail- movement.
Mitochondria- provides energy for tail movement.
Acrosome- contains enzymes that digest the egg cell membrane.

Question 6

Cell specialisation

Nerve cell specialisation.

Answer 6

Long axon- allows electrical impulses to be transmitted all over the body from the central nervous system.
Dendrites- from the cell body connect to and receive impulses from other nerve cells, muscles and glands.
Myelin sheath- insulates the axon and speeds up the transmission of impulses along the nerve cell.

Question 7

Cell specialisation

Muscle cell specialisation.

Answer 7

Arrangement of protein filaments- allows them to slide over each other to produce muscle contraction.
Mitochondria- provide energy for muscle contraction.
Merged cells in skeletal muscle- allow muscle fibre contraction in unison.

Question 8

Cell specialisation

Root hair cell specialisation.

Answer 8

Large surface area- absorbs water and nutrients from the surrounding soil.
Thin walls- don’t restrict water absorption.

Question 9

Cell specialisation

Xylem cell specialisation.

Answer 9

No upper or lower margins between cells- to provide a continuous route for water to flow.
Thick, woody side walls- strengthen their structure and prevent collapse.

Question 10

Cell specialisation

Phloem cell specialisation.

Answer 10

Sieve plates- let dissolved amino acids and sugars be transported up and down the stems.
Companion cells- provide the energy needed for active transport of substances along the phloem.

Question 11

Cell differentiation

What is cell differentiation and why is it important?

Answer 11

The process by which cells become specialised. It is important because it allows the production of different tissues and organs that perform various vital functions in the human body.

Question 12

Cell differentiation

What is the purpose of cell division in mature animals?

Answer 12

Repair and replacement of cells.

Question 13

Cell differentiation

What changes does a cell go through as it differentiates?

Answer 13

Becomes specialised through acquisition of different sub-cellular structures to enable a specific function to be performed by the cell.

Question 14

Microscopy

Define magnification.

Answer 14

The number of times bigger an image appears to the size of the real object.

Question 15

Microscopy

Define resolution.

Answer 15

The smallest distance between two objects that can be distinguished.

Question 16

Microscopy

How does a light microscope work?

Answer 16

Passes a beam of light through a specimen which travels through the eyepiece lens, allowing the specimen to be observed.

Question 17

Microscopy

What are the advantages of light microscopes?

Answer 17

• inexpensive
• easy to use
• portable
• observe both living and dead specimens

Question 18

Microscopy

What are the disadvantages of light microscopes?

Answer 18

• Limited resolution

Question 19

Microscopy

How does an electron microscope work?

Answer 19

It uses a beam of electrons which are focused using magnets. The electrons hit a flourescent screen which emits visible ligh, producing an image. \

Question 20

Microscopy

What are the advantages of electron microscopes?

Answer 20

• Greater magnification
• Greater resolution

Question 21

Microscopy

How have electron microscopes enabled scientists to dveleoping their understanding of cells?

Answer 21

• Allow small sub-cellular structures to be observed in detail
• Enable scientists to develop more accurate explanations about how cell structure relates to function

Question 22

Microscopy

What are the disadvantages of electron microscopes?

Answer 22

• Expensive
• Large so less portable
• Requires training to use
• Only dead specimens can be observed

Question 23

Microscopy

How can magnification be calculated?

Answer 23

image size / actual size

Question 24

# Culturing microorganisms How do bacteria multiply and how often?

Answer 24

* Binary fission * Once every 20 mins if enough nutrients are available and the temperature is suitable

Question 25

# Culturing microorganisms State 2 ways in which bacteria can be grown.

Answer 25

* Nutrient broth solution * Colonies on an agar gel plate

Question 26

# Culturing microorganisms Describe the preparation of an uncontaminated culture using aseptic techniques.

Answer 26

1. Use pre-sterilised plastic petri dishes or sterilise glass petri dishes and agar gel before using with an autoclave 2. Pour the sterile agar gel into the petri dish and allow time to set 3. Sterilise the inoculating loop by passing it through a bunsen burner flame 4. Dip the inoculating loop into the solution of microorganisms and make streaks with the loop on the surface of the agar 5. Put the lid on the petri dish and secure it with tape. Label accordingly then turn and store upside down 6. Incubate the culture at 25'C in school laboratories

Question 27

# Culturing microorganisms Why must petri dishes and equipment be sterilised before use?

Answer 27

To kill any bacteria already present.

Question 28

# Culturing microorganisms Why must the petri dish lid be secured with tape and stored upside down?

Answer 28

* Stops bacteria in the air contaminating the culture * The lid is not fully sealed to prevent the growth of anaerobic bacteria in a lack of oxygen * Upside down to prevent condensation from forming and dripping down onto the colonies

Question 29

# Culturing microorganisms What is the formula used to calculate cross-sectional area of a bacterial colony or clear area around a bacterial colony?

Answer 29

πr^2

Question 30

# Culturing microorganisms How is the number of bacteria in a population after a certain time calculated from the mean division time?

Answer 30

Number of bacteria in population at the end of time period= number of bacteria in population at the beginning of time period X 2^number of divisions in time period