3.2.1 Cell Structure

Question 1

Structure of cell surface membrane (4)

Answer 1

• Phospholipid bilayer: ‘fluid mosaic’
  (a) cholesterol embedded within.
  (b) glycoproteins and glycolipids attached on outside surface.
  (c) proteins attached within or on surface of bilayer.

Question 2

Function of cell surface membrane (3)

Answer 2

• Isolates cytoplasm from extracellular environment.
• Selectively permeable to regulate transport of substances.
• Receptors on surface enable cell-to-cell communication and recognition.

Question 3

Structure of nucleus (5)

Answer 3

• Nuclear envelope: semi permeable double membrane - outer membrane continuous with the RER and studded with ribosomes.
• Nuclear pores: channels within nuclear envelope.
• Nucleoplasm: jelly-like substance containing enzymes and nucleotides needed for DNA and RNA synthesis.
• Nucleolus: dense; made of RNA and proteins which assemble into ribosomes.
• Chromatin: linear DNA coiled around histone protein that condense to form visible chromosomes during cell division.

Question 4

Function of nucleus (3)

Answer 4

• Controls cell’s activity: contains DNA with instructions to produce enzymes via mRNA transcription.
• Nucleoplasm contains enzymes and nucleotides needed for RNA and DNA synthesis
• Nucleolus makes rRNA and synthesises ribosomes.
• Nuclear pores regulate transport of molecules between nucleus and cytoplasm.

Question 5

Structure of mitochondria (2)

Answer 5

• Double membrane: inner membrane folded to form cristae.
• Liquid matrix: contains small 70S ribosomes, mtDNA and enzymes.

Question 6

Function of mitochondria (2)

Answer 6

• DNA to code for enzymes needed in glycolysis.
• Site of aerobic respiration: produces ATP for energy release.

Question 7

Structure of Golgi apparatus (2)

Answer 7

• Folded membrane form cisternae: fluid-filled, membrane bound sacs
• Secretary vesicles pinch off from the cisternae.

Question 8

Function of Golgi apparatus (4)

Answer 8

• Modifies proteins and lipids from ER through processes like glycosylation.
• Packages molecules for secretion from the cell such as enzymes, carbohydrates or hormones.
• Produces and packages lysosomes: vesicles with digestive enzymes for breaking down waste.
• Synthesizes complex polysaccharides in plants for plant cell wall formation.

Question 9

Structure of lysosomes (2)

Answer 9

• Contains lysozymes
• Surrounded by membrane to keep enzymes separate from cell cytoplasm.

Question 10

Function of lysosomes (1)

Answer 10

Releases lysozymes to break down/hydrolyse pathogens and waste materials, like old cells and organelles.

Question 11

Structure of ribosomes (4)

Answer 11

• Made of protein and rRNA
• Made up of large and small sub units
• Not membrane bound
• 80S - large ribosomes found in eukaryotic cells
• 70S - small ribosomes found in prokaryotic cells, mitochondria and chloroplasts

Question 12

Function of ribosomes (2)

Answer 12

• Site of protein synthesis (specifically translation).
• Float free in cytoplasm or bound to RER.

Question 13

Structure of rough & smooth endoplasmic reticulum (2)

Answer 13

• Network of membranes with fluid-filled space.
• RER cisternae surface covered with ribosomes.

Question 14

Function of rough & smooth endoplasmic reticulum (2)

Answer 14

• RER: synthesises and transport protein
• SER: synthesise, storage and transport of lipids and carbohydrates.

Question 15

Where are chloroplasts found

Answer 15

Plants and algae

Question 16

Structure of chloroplasts (4)

Answer 16

• Thylakoid: fluid filled sacs which are stacked to form grana and linked with lamellae.
• Surrounded by double membrane.
• Filled with fluid called stroma, which contains enzymes for photosynthesis
• Contain starch granules, circular DNA and ribosomes.

Question 17

Function of chloroplasts (1)

Answer 17

Site of photosynthesis: chlorophyll absorbs sunlight for photosynthesis to produce organic substances.

Question 18

Where are cell vacuoles found?

Answer 18

Plants

Question 19

Structure of cell vacuole (2)

Answer 19

• Contains cell sap: weak solution of sugars and salts, among other substances.
• Surrounded by tonoplasts: selectively permeable membrane.

Question 20

Function of cell vacuole (1)

Answer 20

Maintains pressure in cell

Question 21

Structure of centrioles (1)

Answer 21

Hollow cylinders containing microtubules arranged at right angles to each other.

Question 22

Function of centrioles (1)

Answer 22

Produce spindle fibres for cell division

Question 23

How do algal and fungal cells differ from plant cells?

Answer 23

ALGAL

• Same organelles as plant cells but have differently shaped chloroplasts.

FUNGAL

• Do not have chloroplasts.
• Have cell walls made of chitin.

Question 24

Specialised cell

Answer 24

Cells that have unique structures an functions, developed through differentiation, to perform a specific role in a multicellular organism.

Question 25

Tissue

Answer 25

Group of cells with similar structures working together to perform a specific function.

Question 26

Organ

Answer 26

Group of tissues working together to perform a particular function

Question 27

Organ system

Answer 27

Group of organs working together to perform a particular function.

Question 28

Examples of specialised cells

Answer 28

- Erythrocytes - Neutrophils - Palisade

Question 29

Examples of tissues

Answer 29

- Epithelium - Cartilage - Xylem

Question 30

Examples of organs

Answer 30

- Stomach - Pancreas - Leaf

Question 31

Examples of organ systems

Answer 31

- Cardiovascular system - Digestive system - Root system.

Question 32

Specialisation of erythrocytes

Answer 32

- Biconcave shape: large SA:V for faster diffusion - Flexible - No nucleus: more space for haemoglobin to bind to oxygen (higher capacity).

Question 33

Specialisation of neutrophils

Answer 33

- Large - Multi-lobed nucleus - Can move by chemotaxis via receptors

Question 34

Process of protein synthesis and transport

Answer 34

1. DNA - Contains genetic code for proteins; bases in DNA determine sequence of amino acids