Cell Structure

Question 1

Cell theory

Answer 1

1. Cell is the fundamental unit of structure and function
2. All cells arise from pre-existing cells by division
3. Metabolism occurs within cells involving biochemical reactions
4. Cells contain hereditary information (DNA) passed from parent to daughter cell during cell division
5. Similar species have cells with similar chemical composition
6. Living things made up of one or more cells
7. Activity of organism depends on the total activity of independent cells

Question 2

Magnification

Answer 2

Degree to which the viewed image is larger than the specimen

Question 3

Resolution

Answer 3

Minimum distance whereby two points can be distinguished as separate

Question 4

Transmission electron microscope

Answer 4

Study internal structures

Question 5

Scanning electron microscope

Answer 5

Study surface of cells -> 3D image

Question 6

Cell fractionation

Answer 6

Cells homogenised -> centrifuge separates organelles based on size/density

Question 7

Size of organelles (micrometer)
Nucleus
Chloroplast
Mitochondrion
Lysosome
Centrioles
Ribosome

Answer 7

Nucleus: 5-10
Chloroplast: 5-10
Mitochondrion: 1-5
Lysosome: 0.2-1.0
Centrioles: 0.3-0.5
Ribosome: 0.02 (20nm)

Question 8

Overview of cell structure (4)

Answer 8

1. Plasma membrane/cell surface membrane
2. Nucleus
3. Cytoplasm -> Cytosol + organelles + cytoskeleton (framework of protein filaments that give cells their shape)
4. Cell wall

Question 9

Nucleus structure

Answer 9

Spherical
Nuclear envelope -> double membrane + nuclear pores
Chromosomes/chromatin -> DNA + histones -> euchromatin (loosely coiled, active) + heterochromatin (tightly coiled, not active)

Question 10

Nucleus function

Answer 10

1. Contains hereditary material (DNA) of organism

2. Controls activities of the cell by regulating protein synthesis

Question 11

Nucleolus structure

Answer 11

Densely stained granules
One or more nucleoli per nucleus
Large concentration of DNA, rRNA and proteins

Question 12

Nucleolus function

Answer 12

Synthesis of rRNA

Assembly of rRNA and ribosomal proteins into ribosomal subunits

Question 13

Ribosome structure

Answer 13

Small subunit + large subunit
Ribosomal RNA + proteins
1. Freely floating in the cytosol (free ribosomes)
2. Attached to outer surface of rER (bound ribosomes)
Prokaryotes -> 70S
Eukaryotes -> 80S

Question 14

Ribosome function

Answer 14

Protein synthesis -> translation of mRNA to protein
Free ribosomes -> proteins that function within cytosol
Bound ribosomes -> proteins for:
1. Secretion out of cell
2. Packaging within organelles
3. Insertion into membrane

Question 15

Endomembrane system (5)

Answer 15

1. Nuclear envelope
2. Endoplasmic reticulum (ER)
3. Golgi Apparatus
4. Lysosome + Vesicles
5. Plasma membrane

Question 16

Nuclear envelope structure + function

Answer 16

Perforated by numerous nuclear pores, continuous with ER

Allow regulated passage of substances into or out of the nucleus

Question 17

Endoplasmic reticulum structure

Answer 17

Extensive network of membranous tubules and sacs called cisternae

Question 18

Rough endoplasmic reticulum structure

Answer 18

Bound ribosomes that stud outer surface -> rough
Signal peptide recognised by signal recognition particle -> bring ribosome to rER -> receptor protein
Cisternae flattened than sER

Question 19

Rough endoplasmic reticulum function (4)

Answer 19

1. Proteins synthesise by bound ribosomes fold into native 3D conformation as they enter cisternal space
2. Glycosylation (add carbs) to form glycoproteins
3. Transport of proteins in transport vesicles
   (i) Secretion out of the cell
   (ii) Packaging into organelles
   (iii) Targeted for insertion into plasma membrane
4. Membrane factory -> grows by adding membrane proteins and phospholipids to own membrane -> transferred in the form of transport vesicles

Question 20

Smooth endoplasmic reticulum structure

Answer 20

Appears smooth as it lacks bound ribosomes

Cisternae more tubular

Question 21

Smooth endoplasmic reticulum function (4)

Answer 21

1. Synthesise carbohydrates and lipids
2. Break down glycogen to glucose in liver cells
3. Detoxify drugs and poison in liver cells
4. Store Ca2+ ions in muscle cells

Question 22

Golgi apparatus structure

Answer 22

Cisternae + Golgi vesicles
Convex/’cis’ face -> vesicles fuse with it
Concave/’trans’ face -> vesicles pinch off

Question 23

Golgi apparatus function (5)

Answer 23

Modifying, sorting and packaging

1. Glycosylation -> glycoproteins and glycolipids
2. Modify/cleave existing glycoproteins and glycolipids
3. Form lysosomes
4. Produce polysaccharides
5. Sorts and targets completed material to different parts of the cell or for secretion

Question 24

Lysosome structure

Answer 24

Single membrane
Hydrolytic enzymes made by bound ribosomes on rER and processed in GA -> bud off from there
Acidic

Question 25

Lysosome function (4)

Answer 25

1. Digestion of material taken in by endocytosis -> fuse with vesicles/vacuoles 2. Autophagy -> breakdown of unwanted structures 3. Release enzymes outside cell by exocytosis 4. Autolysis -> contents of many lysosomes released within the cell simultaneously Useful products absorbed into cytoplasm; Unwanted products released into external medium by exocytosis

Question 26

Mitochondrion structure

Answer 26

Rod-shaped Double membrane Outer membrane smooth Inner membrane highly unfolded to form numerous cristae -> large surface area Matrix + inter membrane space Contains 70S ribosomes, circular DNA and enzymes

Question 27

Mitochondrion function

Answer 27

Site of cellular respiration -> generate ATP | Krebs cycle in matrix, oxidative phosphorylation in cristae

Question 28

Chloroplast structure

Answer 28

Lens shaped Double membrane Thylakoids -> grana (stacks) Chlorophyll, photosynthetic pigments, enzymes, photosystems on thylakoid membrane Stroma contains circular DNA, ribosomes, enzymes and starch grains

Question 29

Chloroplast function

Answer 29

Site of photosynthesis

Question 30

Vacuole structure

Answer 30

Large vesicles derived from ER and GA Fluid-filled sac bound by single membrane Animal -> smaller and more numerous Plant -> large central vacuole (tonoplast) which contains cell sap

Question 31

Vacuole function

Answer 31

Animal Food vacuoles formed by phagocytosis enclose material for digestion by lysosome Fresh water protists -> contractile vacuoles -> pump excess water out ``` Plant Maintain turgor pressure Cell growth -> increase with minimal increase in cytoplasm Store waste products Food storage in seeds ```

Question 32

Microtubule structure

Answer 32

``` Hollow rods (25nm diameter) Globular protein (tubulin) -> dimer (2 subunits) Stiff and run straight course ```

Question 33

Microtubule function (4)

Answer 33

1. Help maintain shape of cell (cytoskeleton) 2. Intracellular transport 3. Chromosome movement in cell division (spindle fibres) 4. Structural component of centrioles, cilia and flagella

Question 34

Centrioles structure

Answer 34

Pair of cylindrical, rod-like structures positioned at right angles 9 triplets of microtubules arranged in a ring Found in region known as centrosome Absent in higher plant cells (Microtubule organising centre)

Question 35

Centrioles function

Answer 35

Replicate during cell division | Play role in nuclear division by helping to organise formation of spindle fibres, needed for separation of chromosomes