COMPREHENSIVE REVIEW Flashcards
Discuss possible exceptions to cell theory
- 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
Eukaryotic cells have intracellular and extracellular components. State the functions of one named extracellular component.
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;
Explain how the surface are to volume ratio influences cell sizes.
- 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
Outline differentiation of cells in a multicellular organism.
- 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
Describe the importance of stem cells in differentiation.
- 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;
State one function of each of the following organelles: lysosome, Golgi apparatus, rough endoplasmic reticulum, nucleus, mitochondrion.
- 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
Distinguish between the structure of plant and animal 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
animal cells
•have centrioles, plant cells do not
•have cholesterol in the cell membrane, plant cells do not
•plant cells are generally have a fixed shape/ more regular whereas animal cells are more rounded
Using a table, compare the structures of prokaryotic and eukaryotic cells.
- DNA: P: naked/loop of DNA; E: associated with protein/histones/nucleosomes/DNA in chromosomes
- location of DNA: P: in cytoplasm/nuceloid/no nucleus; E: within a nucleus/nuclear membrane
- membrane bound organelles: P: none; E: present
- ribosomes: P: 70S ; E: 80S
- plasma membrane: P & E: same structure within both groups
- cell wall: P: peptidoglycan/not cellulose/not chitin; E: cellusose/chitin/not peptidoglycan
- respiratory structures: P: no mitochondria; E: mitochondria
- pili: P: pili present E: pili absent;
- plasmids: P: plasmids (sometimes) present E:plasmids absent;
- flagella: P: flagella solid E: flagella flexible/membrane-bound;
Explain how the structure and properties of phospholipids help to maintain the structure of cell membranes. 9 marks
Explain how the structure and properties of phospholipids help to maintain the structure of cell membranes. 9 marks
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
A suitable annotated diagram may incorporate all or many of the above points. Award 5 marks maximum for a suitable diagram that is labelled correctly.
- 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
- hydrophilic/ hydrophobic layers restrict entry/ exit of substances
Explain the role of vesicles in transportation of materials within cells.
- 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 plsma membrane releases/secretes contents
- exocytosis
Describe the process of active transport. 4 marks
- uses/ requires energy/ ATP
- goes against concentration gradient/ lower to higher concentration
- requires a protein in the cell membrane/ pump/ carrier protein (reject channel)
- hydrolysis of ATP/ ATP –> ADP + phosphate
- involves a conformational change in the pump/ protein/ diagram to show this
Outline the ways in which substances move passively across membranes. 5 marks
- diffusion (is a method of passive transport across the membrane)
- pore/ channel proteins for facilitated diffusion/ to allow hydrophilic particles across
- movement from high to low concentration/ down the concentration gradient
- membrane must be permeable to the substance diffusing
- oxygen/ other named example of a substance than can diffuse through membranes
- osmosis is movement of/ diffusion of water through a membrane
- from a region of lower to a region of higher solut concentration/ higher to lower water potential
- membranes are (nearly) always freely permeable to water
Distinguish between active and passive movements of materials across plasma membranes, using named examples. 4 marks
- 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;
- passive: oxygen across alveoli / other example, whereas, active transport: glucose absorption in ileum / other example;
Outline, with an example, the process of exocytosis.
- 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.;
Explain the reasons for cell division in living organims. 8 marks
- to increase the number of cells in an organism
- to allow differentiation/ cell specialization
- for greater efficiency
- to replace damaged/ lost cells
- example
- binary fission
- asexual reproduction of unicellular organisms
- gamete/ spore formation
- cells only arise from pre-existing cells
- refer to Virchow
- cells cannot grow beyond a certain size
- surface area to volume ratio becomes too small
- transport across the membrane too slow
- example
- nucleus cannot control the cell
