Topic 1: Cell Biology

Question 1

Discuss possible exceptions to cell theory. [4]

Answer 1

 skeletal muscle fibers are larger/have many nuclei/are not typical cells
 fungal hyphae are (sometimes) not divided up into individual cells
 unicellular organisms can be considered acellular
 because they are larger than a typical cell/carry out all functions of life
 some tissues/organs contain large amounts of extracellular material
 e.g. vitreous humor of eye/ mineral deposits in bone/ xylem in trees/other example
 statement of cell theory/all living things/most tissues are composed entirely of true cells

Question 2

Eukaryotic cells have intracellular and extracellular components. State the functions of one named extracellular component. [4]

Answer 2

name of component: 1 max
 e.g. plant cell wall/cellulose/interstitial
 matrix/basement membrane/glycoprotein/bone matrix;
functions: 3 max
EITHER
 e.g. (plant cell wall) strengthens/supports the cell/plant (against gravity);
 prevents the entry of pathogens;
 maintains the shape of plant cells;
 allows turgor pressure/high pressure to develop inside the cell;
 prevents excessive entry of water to the cell;
OR
 helps cells to stick together/adhere;
 needed to hold cells/tissues together / example of cells/tissues holding together;
 forms interstitial matrix / forms basement membrane to support single layers of cells;
 e.g. around a blood capillary;
 forms (part of the) filtration membrane in the glomerulus;

Question 3

Explain how the surface are to volume ratio influences cell sizes. [3]

Answer 3

 small cells have larger ratio (than larger cells)/ratio decreases as size increases
 surface area/membrane must be large enough to absorb nutrients/oxygen/substances needed
 surface area/membrane must be large enough to excrete/pass out waste products
 need for materials is determined by (cell) volume
 cell size is limited (by SA/Volume ratio)/cells divide when they reach a certain size
 reference to diffusion across/through membrane/surface area

Question 4

Outline differentiation of cells in a multicellular organism. [4]

Answer 4

 differentiation is development in different/specific ways
 cells carry out specialized functions/become specialized
 example of a differentiated cell in a multicellular organism
 cells have all genes/could develop in any way
 some genes are switched on/expressed but not others
 position/hormones/cell-to-cell signals/chemicals determine how a cell develops
 a group of differentiated cells is a tissue

Question 5

Describe the importance of stem cells in differentiation. [3]

Answer 5

 stem cells are undifferentiated cells;
 embryo cells are stem cells;
 stem cells can differentiate in many/all ways / are pluripotent/totipotent;
 differentiation involves expressing some genes but not others;
 stem cells can be used to repair/replace tissues/heal wounds;

Question 6

State one function of each of the following organelles: lysosome, Golgi apparatus, rough endoplasmic reticulum, nucleus, mitochondrion. [5]

Answer 6

 lysosome: hydrolysis/digestion/break down of materials (macromolecules)
 Golgi apparatus: synthesis/sorting/transporting/secretion of cell products
 rough endoplasmic reticulum: site of synthesis of proteins (to be secreted)/ intracellular transport of polypeptides to Golgi apparatus
 nucleus: controls cells activities/mitosis/replication of DNA/transcription of DNA (to RNA)/directs protein synthesis
 mitochondrion: (aerobic) respiration/generates ATP

Question 7

Distinguish between the structure of plant and animal cells. [6]

Answer 7

Award 1 mark per difference
plant cells
 have cell walls, animals do not
 have plastids/ chloroplasts, animals do not
 have a large central vacuole, animals do not
 store starch, animal cells store glycogen
 have plasmodesmata, animal cells do not
 fixed shape / more regular shape
animal cells
 have centrioles, plant cells do not
 have cholesterol in the cell membrane, plant cells do not
 more rounded

Question 8

Explain how the structure and properties of phospholipids help to maintain the structure of cell membranes. [9]

Answer 8

phospholipid structure
 hydrophobic tail/hydrophilic head
 head made from glycerol and phosphate
 tail made from two fatty acids
 saturated/ unsaturated fatty acid (in tail)
arrangement in membrane
 phospholipids form a bilayer
 heads face outside the membrane/ tails face inside the membrane/ hydrophic interior/ hydrophilic exterior of membrane
 phospholipids held together by hydrophobic interactions
 phospholipid layers are stabilized by interaction of hydrophilic heads and surrounding water
 phospholipids allow for membrane fluidity/ flexibility
 fluidity/ flexibility helps membranes to be (functionally) stable
 phospholipids with short fatty acids/ unsaturated fatty acids are more fluid
 fluidity is important in breaking and remaking membranes (e.g. endocytosis/ exocytosis)
 phospholipids can move about/ move horizontally/ “flip flop” to increase fluidity

Question 9

Explain the role of vesicles in transportation of materials within cells. [8]

Answer 9

 vesicles are membrane bound packages/droplets
 formed by pinching off/budding off a piece from a membrane
 can carry proteins
 rough ER synthesizes proteins
 proteins enter/accumulate inside the ER
 transported to Golgi apparatus for processing
 targeted to/transported to specific cellular organelles
 fuse with membrane of organelle so contents of vesicle join the organelle
 transported to the plasma membrane
 fuses with plasma membrane releases/secretes contents
 exocytosis

Question 10

Distinguish between active and passive movements of materials across plasma membranes, using named examples. [4]

Answer 10

 passive: oxygen across alveoli / other example, whereas, active transport: glucose absorption in ileum / other example;
 passive: diffusion / osmosis / facilitated diffusion, whereas, active transport: ion pumps / exocytosis / pinocytosis / phagocytosis
 a second passive method (from above), whereas, active transport: a second active method; (from above)
 passive: does not require energy, whereas, active transport: requires energy/ATP;
 passive: down concentration gradient, whereas, active transport: against concentration gradient;
 passive: no pumps needed, whereas, active transport: requires protein pumps;

Question 11

Outline, with an example, the process of exocytosis. [5]

Answer 11

 vesicles carry material to plasma membrane;
 vesicle fuses with membrane;
 (by joining of) phospholipid bilayers;
 aided by the fluidity of the membrane;
 material released/expelled from the cell;
 membrane flattens;
 name of example e.g. exocytosis of neurotransmitter / exocrine secretion/endocrine secretion / hormone secretion / release of cortical granules;
 outline of example: (in the presence of calcium), neurotransmitter vesicles release their contents into the synapse / hormones released from one cell have an effect on another cell etc.;

Question 12

Outline the processes that occur in a cell during interphase, including those needed to prepare for mitosis. [4]

Answer 12

	DNA replication
	DNA transcription
	enzyme/ protein synthesis
	biochemical reactions/ example of a biochemical reaction
	cell respiration
	growth
	organelles replicated