Cell structure

Question 1

Define terms eukaryotic and prokaryotic cell

Answer 1

Eukaryotic: DNA is contained in a nucleus, contains membrane-bound specialised organelles

Question 2

State the relationship between a system and specialised cells

Answer 2

Specialised cells -> tissues that perform specific functions -> organs made of several tissue types -> organ systems

Question 3

Describe structure and function of cell-surface membrane

Answer 3

‘Fluid-mosaic’ phospholipid bilayer with extrinsic & intrinsic proteins embedded
- Isolates cytoplasm from extracellular environment
- Selectively permeable to regulate transport of substances
- Involved in cell signalling/ cell recognition

Question 4

Explain role of cholesterol, glycoproteins & glycolipids in the cell-surface membrane

Answer 4

Cholesterol: steroid molecule connects phospholipids & reduces fluidity
Glycoproteins: cell signalling, cell recognition (antigens) & binding cells together
Glycolipids: cell signalling & cell recognition

Question 5

Describe structure of nucleus

Answer 5

• Surrounded by nuclear envelope, a semi-permeable double membrane
• Nuclear pore allow substances to enter/ exit
• Dense nucleolus made of RNA & proteins assembles ribosomes

Question 6

Describe function of nucleus

Answer 6

• Contains DNA coiled around chromatin into chromosomes
• Controls cellular processes: gene expression determines specialisation & site of mRNA transcription, mitosis, semi-conservative replication

Question 7

Describe structure of mitochondrion

Answer 7

• Surrounded by double membrane folded inner membrane forms critae: site of electron transfer chain
• Fluid matrix: contains mitochondrial DNA, respiratory enzymes, lipids, proteins

Question 8

Describe structure of chloroplast

Answer 8

• Vesicular plastid with double membrane
• Thylakoids: flattened discs stack to form grana; contain photosystems with chlorophyll
• Intergranal lamellae: tubes attach thylakoids in adjacent grana
• Stroma: fluid-filled matrix

Question 9

State function of mitochondria & chloroplasts

Answer 9

• Mitochondria: site of aerobic respiration to produce ATP
• Chloroplasts: site of photosynthesis to convert solar energy to chemical energy

Question 10

Describe structure & function of Golgi Apparatus

Answer 10

Planar stacks of membrane-bound, flattened sacs cis face aligns with rER
Molecules are processed in cisternae vesicles bud off trans face via exocytosis
- Modifies & packages proteins for export
- Synthesises glycoproteins

Question 11

Describe structure & function of lysosome

Answer 11

Sac surrounded by single membrane embedded H+ pump maintains acidic conditions contains digestive hydrolase enzymes glycoprotein coat proteins cell interior:
- Digests contents of phagosome
- Exocytosis of digestive enzymes

Question 12

Describe structure & function of ribosome

Answer 12

Formed of protein & rRNA free in cytoplasm or attached to ER
- Site of protein synthesis via translation: large subunit - joins amino acids.
small subunit - contains mRNA binding site

Question 13

Describe structure & function of endoplasmic reticulum (ER)

Answer 13

Cisternae: network of tubules & flattened sacs extends from cell membrane through cytoplasm & connects to nuclear envelope:

• Rough ER: many ribosomes attached for protein synthesis & transport
• Smooth ER: lipid synthesis

Question 14

Describe structure of cell wall

Answer 14

• Bacteria: made of polysaccharide murein
• Plants: made of cellulose microfibrils plasmodesmata allow molecules to pass between cells, middle lamellae acts as boundary between adjacent cell walls