A2.2 Cell structure

Question 1

Cells as the basic structural unit of all living organisms (A2.2.1)

Answer 1

All living things are composed of cells.
Cells come from preexisting cells.
The cell is the basic unit of life.

Question 2

Microscopy skills (A2.2.2)

Answer 2

Magnification = size of image/actual size of specimen

Make sure all units are the same.

Question 3

Milimetres to micrometres (A2.2.2)

Answer 3

x1000 (and vice versa)

Question 4

Stains and fluorescence (A2.2.3)

Answer 4

Stains: coloured substances that bind to some chemicals but not others.

Fluorescence: when a substance absorbs light then re-emits it at a longer wavelength.

Question 5

Fluorescent microscopes and immunofluorescence (A2.2.3)

Answer 5

Microscopes have intense light sources (LEDs/lasers) which emit single wavelength. Light absorbed + re-emitted by sample -> generates bright images.

Immunofluorescence: Antibodies that bind to particular antigens in cell are produced. Fluorescent markers of diff. colours linked to antibodies. Multicoloured fluorescent image produced -> shows chems located.

Question 6

Freeze-fracture electron microscopy (A2.2.3)

Answer 6

Produce images of surfaces within cells.

Sample rapidly freezed (liq propane). Steel blade fractures sample between membrane. Then etched: ice at surface removed by vaporization -> enhance texture.

Vapour platinum/carbon fired onto surface at 35° to form coating. Creates a replica.

Question 7

Cryogenic electron microscopy (A2.2.3)

Answer 7

For researching the structure of proteins.

Thin layer protein solution flash-frozen on grid (using liq ethane) + put in electron microscope -> detectors capture electron transmission patterns of individual proteins.

Patterns combined using computer algorithm-> 3D image of protein at freezing.

Question 8

Structures common to cells in all living organisms - plasma membrane (A2.2.4)

Answer 8

Outer boundary, controlls entry + exit of substances, prevents unwanted/toxic ones entering.

Can pumps substances in against a conc. gradient + helps maintain concs. different from surrounding environment.

Question 9

Structures common to cells in all living organisms - cytoplasm (A2.2.4)

Answer 9

Water = main component, many substances
dissolved/suspended. Enzymes catalyse diff chem reactions -> metabolism.

Metabolism provides cell w/ energy, produces all proteins + substances that make up cell structure.

Question 10

Structures common to cells in all living organisms - DNA (A2.2.4)

Answer 10

DNA can be copied + passed on to daughter cells + generations = heritable. Genes contain info for cell to carry out functions.

Plant + animal cells have a nucleus, bacteria store DNA in cytoplasm.

Question 11

Prokaryote cell structure - cell wall (A2.2.5)

Answer 11

Thicker + stronger than membrane. Protects cell, maintains shape + supports membrane to prevent bursting. Contains peptidoglycan.

Question 12

Prokaryote cell structure - cytoplasm/ribosome (A2.2.5)

Answer 12

Cytoplasm w/ no compartmentalization. No cytoplasmic organelles apart from 70S ribosomes.

Electron micrographs darker region of cytoplasm = contain ribosomes, enzymes + other proteins.

Question 13

Prokaryote cell structure - DNA storage (A2.2.5)

Answer 13

Only single “naked” DNA molecule that forms a loop or circle.

Electron micrographs lighter region of cytoplasm = nucleoid (has DNA).

Question 14

Eukaryote cell structure - cell wall, cytoplasm divison. (A2.2.6)

Answer 14

Some eukaryotes have a cell wall. Have a compartmentalized cytoplasm, separated by single or double membranes.

Question 15

Eukaryote cell structure - nucleus (A2.2.6)

Answer 15

Compartment holds cell’s chromosomes. Double membrane w/ pores through it.

Chromosome = one long DNA molecule attached to histones. DNA is linear.

Question 16

Eukaryote cell structure - ribosomes (A2.2.6)

Answer 16

80S ribosomes, larger in size and more mass. Sink quicker than when centrifuged.

Question 17

Eukaryote cell structure - mitochondria (A2.2.6)

Answer 17

In cytoplasm. Has double membrane. Inner membrane folded inwards = increase SA.

Produces ATP (cell’s energy currency) by converting glucose in aerobic cell resp.

Question 18

Processes of life - homeostasis (A2.2.7)

Answer 18

Maintenance of a constant internal environment in an organism.

Question 19

Processes of life - metabolism (A2.2.7)

Answer 19

The sum of all the biochemical reactions that occur in a living organism.

Question 20

Processes of life - nutrition (A2.2.7)

Answer 20

Supplying the nutrients required for energy, growth and repair in an organism.

Question 21

Processes of life - excretion (A2.2.7)

Answer 21

Removal of waste products of metabolism from an organism.

Question 22

Processes of life - growth (A2.2.7)

Answer 22

An increase in size or number of cells.

Question 23

Processes of life - response to stimuli (A2.2.7)

Answer 23

Perception of stimuli and carrying out appropriate actions in response.

Question 24

Processes of life - reproduction (A2.2.7)

Answer 24

Production of offspring, either sexually or asexually.

Question 25

A2.2.8 Differences in eukaryotic cell structure (animals, fungi, plants) - Plastids

Answer 25

Organelles with two outer membranes and internal membrane sacs. Only plants have them (e.g. chloroplast).

Question 26

A2.2.8 Differences in eukaryotic cell structure (animals, fungi, plants) - cell wall

Answer 26

Rigid layer outside plasma membrane to strengthen and protect the cell.

Fungi = composed of chitin
Plants = composed of cellulose

Question 27

A2.2.8 Differences in eukaryotic cell structure (animals, fungi, plants) - vacuole

Answer 27

A flexible fluid-filled compartment, has a single membrane.

Animals = temporary, expel excess water, or digest food/pathogens from endocytosis.

Plants, fungi = large, permanent, for storage of substances and pressurising the cell.

Question 28

A2.2.8 Differences in eukaryotic cell structure (animals, fungi, plants) - centrioles

Answer 28

Cylindrical organelles that organize microtubules (the cell’s skeletal system), which determines nucleus placement.

Animals = important to mitosis and cilia/flagella base structure.

Plants, fungi = absent, except in […] w/ swimming male gametes

Question 29

A2.2.8 Differences in eukaryotic cell structure (animals, fungi, plants) - Undulipodia

Answer 29

Cilia and flagella generate cell movement or fluid movement around the cell.

Animals = in many animal cells.

Plants, fungi = absent, except male gametes that swim using flagella.

Question 30

A2.2.9 Atypical cell structure in eukaryotes - Skeletal muscle cells

Answer 30

A syncytium forms when cells fuse, as in muscle fibers. Cells, each w/ a nucleus, divide into columns, then fuse.

Question 31

A2.2.9 Atypical cell structure in eukaryotes - Red blood cells

Answer 31

Lack a nucleus. When developing in bone marrow, nucleus moves to the edge of the cytoplasm, is pinched off, and destroyed by phagocytes. Cell is smaller + more flexible, but can’t repair damage. Life: 100-120 days.

Question 32

A2.2.9 Atypical cell structure in eukaryotes - Aseptate fungal hyphae

Answer 32

Coenocyte, an unusually large multinucleate structure, forms in […] when the nucleus divides repeatedly w/out cell division.

These cells are aseptate, as they lack the septa walls which make cells uninucleate.

Question 33

A2.2.9 Atypical cell structure in eukaryotes - Phloem sieve tube elements

Answer 33

Sieve tube elements in plant phloem are anucleate, with little cytoplasm and few organelles, resulting in low resistance to substance movement.

Question 34

A2.2.12 (HL) Origin of eukaryotic cells by endosymbiosis - defenition endosymbiosis

Answer 34

Whereby one cell is engulfed by another and becomes assimilated into its cellular structure.

Question 35

A2.2.12 (HL) Origin of eukaryotic cells by endosymbiosis - mitochondria

Answer 35

Prokaryotic ancestor engulfed an aerobic bacterium, which over time lost its independent utility and developed into the mitochondria.

Question 36

A2.2.12 (HL) Origin of eukaryotic cells by endosymbiosis - chloroplast

Answer 36

Prokaryotic ancestor engulfed a photosynthetic cyanobacterium, which over time lost its independent utility and developed into the chloroplast.

Question 37

A2.2.12 (HL) Origin of eukaryotic cells by endosymbiosis - evidence

Answer 37

Have double membrane (outer may have vesicular origin).

Both organelles susceptible to certain antibiotics (target prokaryotic features). Have their own DNA, naked and circular. Both have 70S ribosomes.

Divide similar to binary fission (bacterial).

Question 38

A2.2.13 (HL) Cell differentiation as the process for developing specialized tissues in multicellular organisms

Answer 38

Emergent properties—which arise from cell specialisation—result from the synergistic actions of individual cells.

Cells specialize by expressing different genes, coordianted by external signals or environmental changes.

Question 39

A2.2.14 (HL) Evolution of Multicellularity - survival advantages

Answer 39

Allows an organism to exceed size limits imposed by SA:Vol ratio limitations.

Have longer lifespans as the organism can survive the death of an individual cell.

Fosters complexity through differentiation of cell types within an organism.