AS Cell Structure and Division

Question 1

Name the organelles present in both animal and plant cells and the 3 organelles only present in plant cells

Answer 1

Both:

• Cell surface (plasma) membrane
• Nucleus
• RER - rough endoplasmic reticulum
• SER - smooth endoplasmic reticulum
• Lysosomes
• Ribosomes
• Golgi apparatus
• Golgi vesicles
• Mitochondria

Plant cells only:

• Chloroplasts
• Vacuole
• Cell wall with plasmodesmata

Question 2

Describe the structure of algal and fungal cells compared to plant cells

Answer 2

Algal cells:
- Same organelles as plant cells
Fungal cells:
- Cell walls made of chitin (not cellulose)
- Don’t have chloroplasts (don’t photosynthesise)

Question 3

Describe the structure and function of the cell-surface membrane

Answer 3

Structure:
- Found on surface of animal cells and inside the cell wall of other cells
- Mainly made of lipids and proteins
Function:
- Regulates movement of substances in and out cell
- Has receptor molecules - respond to chemicals

Question 4

Describe the structure and function of the nucleus

Answer 4

Structure:
- Surrounded by nuclear envelope - contains pores
- Contains chromosomes made from protein-bound linear DNA
- Contains nucleolus
Function:
- Controls cell activities - controlling transcription of DNA
- DNA contains instructions to make proteins
- Pores allow substances (RNA) to move in and out
- Nucleolus makes ribosomes

Question 5

Describe the structure and function of mitochondria

Answer 5

Structure:
- Double membrane - inner one folds to form cristae
- Contains matrix - has enzymes for respiration
Function:
- Site of aerobic respiration - ATP produced
- Found in active cells - require lots of energy

Question 6

Describe the structure and function of chloroplasts

Answer 6

Structure:
- Flattened structure in plant and algal cells
- Double membrane - contains thylakoid membranes
- These stack up into grana - linked together by lamellae
Function:
- Site of photosynthesis
- Some occurs in grana and some in stroma

Question 7

Describe the structure and function of the Golgi apparatus

Answer 7

Structure:
- Fluid-filled, membrane-bound flattened sacs
- Vesicles next to apparatus
Function:
- Processes and packages new lipids
- Makes lysosomes

Question 8

Describe the structure and function of the Golgi vesicles

Answer 8

Structure:
- Fluid-filled sac in cytoplasm
- Produced by Golgi apparatus
Function:
- Stores lipids and proteins made by Golgi apparatus
- Transports them out of cell via plasma membrane

Question 9

Describe the structure and function of lysosomes

Answer 9

Structure:
- Round, surrounded by membrane 
- No internal structure
- Type of Golgi vesicle
Function:
- Contains digestive enzymes - lysozymes
- These digest invading cells or break down worn out components of cell

Question 10

Describe the structure and function of ribosomes

Answer 10

Structure: 
- Very small - no surrounding membrane 
- Free floats in cytoplasm or attached to RER
- Made up of proteins and RNA 
Function:
- Site of protein synthesis

Question 11

Describe the structure and function of the rough endoplasmic reticulum (RER)

Answer 11

Structure:
- System of membranes enclosing fluid-filled space
- Surface covered with ribosomes
Function:
- Folds and processes proteins made at the ribosomes

Question 12

Describe the structure and function of the smooth endoplasmic reticulum (SER)

Answer 12

Structure:
- System of membranes enclosing fluid-filled space 
- No ribosomes
Function:
- Synthesises and processes lipids

Question 13

Describe the structure and function of the cell wall

Answer 13

Structure:
- Rigid structure surrounding plant, algal and fungal cells
- Plants and algae - made mostly of cellulose
- Fungi - made of chitin
Function:
- Supports cells - stops them changing shape

Question 14

Describe the structure and function of the vacuole

Answer 14

Structure:
- Found in cytoplasm of plant cells
- Contains cell sap - solution of sugars and salts
- Surrounding membrane - tonoplast
Function:
- Maintains pressure and keeps cell rigid
- Stops plant wilting
- Involved in isolation of unwanted chemicals inside the cell

Question 15

Explain why the structure of specialised cells may vary in different parts of the body

Answer 15

• Specialised cells carry out specific functions
• Cell structure helps it carry out its function
• If a cell requires lots of energy, it will need more mitochondria. If it requires lots of proteins, it will need more ribosomes

Question 16

How are specialised cells organised?

Answer 16

• Specialised cells grouped together - form tissues
• Tissue - group of cells working together to perform a particular function
• Different tissues work together - form organs
• Different organs make up organ system

Question 17

Name the organelles present in prokaryotic cells

Answer 17

• Plasma membrane
• Ribosomes (smaller than in eukaryotes)
• Cell wall
• Plasmids
• Circular DNA
• Flagellum
• Capsule (some prokaryotes e.g. bacteria)

Question 18

Describe the structure and function of the flagellum

Answer 18

Structure:
- Long, hair-like structure
Function:
- Rotates to make the cell move

Not all prokaryotes have them - some have more than one

Question 19

Describe the structure of circular DNA

Answer 19

Structure:

• No nucleus - DNA free floats in cytoplasm
• One long coiled-up strand
• Not attached to any histone proteins

Question 20

Describe the structure and function of plasmids

Answer 20

Structure:
- Small loops of DNA
Function:
- Contain genes for things like antibiotic resistance - can be passed between prokaryotes

Not always present in prokaryotic cells - some have several

Question 21

Describe the structure and function of the cell wall

Answer 21

Structure:
- Made of a polymer called murein (a glycoprotein)
Function:
- Supports cell and prevents it from changing shape

Question 22

Describe the structure and function of the capsule

Answer 22

Structure:
- Made up of secreted slime
Function:
- Helps protect bacteria from attack by cells of the immune system

Question 23

Describe the structure and function of viruses

Answer 23

Structure:

• Smaller than bacteria - (HIV about 0.1um across)
• No plasma membrane, cytoplasm or ribosomes
• Contain core of genetic material - DNA or RNA
• Capsid - protein coat around core
• Attachment proteins stick out from capsid - let virus cling on to host cell

All viruses invade and reproduce inside host cells

Question 24

Describe the process of binary fission

Answer 24

Cell replicates genetic material before splitting into 2 daughter cells

• Circular DNA and plasmids replicate
• Cells expands - DNA loops move to opposite poles
• Cytoplasm begins to divide - new cell wall forms
• Cytoplasm divides - 2 daughter cells produced - each with one copy of circular DNA and variable plasmids

Question 25

How do viruses use host cells to replicate

Answer 25

- Attachment proteins bind to complementary receptor proteins on host cell surface - Inject their DNA or RNA into host cell - Use cell's ribosomes, enzymes etc. to replicate the viral parts