cells

Question 1

bacterial cells

Answer 1

• cell wall, made from peptidoglycan (a mixture of proteins, lipids and sugars)
• cell membrane
• cytoplasm
• nucleoid/chromosomal DNA, large ring of DNA containing genetic material, it is free-floating (no membrane)
• plasmids, small ring of double-stranded circular DNA
• flagellum, tail like structure used for movement, not found on all bacterial cells
• ribosomes

Question 2

cytoplasm contains…

Answer 2

• dissolved salt ions and sugar molecules
• fat molecules, enzymes, amino acids
• food reserves: glycogen in animal cells, starch in plant cells
• organelles

Question 3

organelles with double membranes

Answer 3

• nucleus
• mitochondria
• chloroplast

Question 4

cell wall

Answer 4

• plants only
• made of cellulose
• freely permeable to water and salts

Question 5

chloroplasts location

Answer 5

only present in photosynthetic plant cells eg. not in root hair cells

Question 6

plasmids

Answer 6

• carries genetic information for specialist cell functions (like antibiotic resistance)
• can replicate and operate independently from the chromosomal DNA
• can be readily moved between different bacterial cells, including for genetic engineering (biotechnology) purposes.

Question 7

difference between eukaryotic and prokaryotic DNA

Answer 7

• DNA in eukaryotic cells are in the nucleus, prokaryotic cells have DNA but no nucleus
• eukaryotic cells usually contain several large chromosomes, but a prokaryotic cell usually only contains one per cell
• DNA in prokaryotic cells are circular with no free ends, but the DNA of eukaryotic cells forms large linear chromosomes with free ends

Question 8

factors affecting diffusion rate

Answer 8

• conc gradient: the greater the difference in concentration of particles, the faster the rate of diffusion
• temperature: higher temp, higher diffusion rates
• distance: the further the particles have to travel, the longer diffusion takes
• size: the smaller the particles, the faster they can diffuse.
• surface area: the larger the surface area, the faster the molecules will diffuse.

Question 9

roles of mitosis

Answer 9

• allows organisms to grow in size by increasing their total number of cells
• allows worn-out and dead cells to be replaced -> tissue repair
• allows some species to reproduce by asexual reproduction

Question 10

mitosis and cancer

Answer 10

• if errors are detected in a cell, such as a mutation in the DNA that cannot be repaired, the cell will be destroyed
• if a cell with errors is not destroyed, the cell cycle will continue and the cell will divide by mitosis
• this may lead to a group of cells that are defective and divide uncontrollably, which can form a tumour -> cancer

Question 11

meiosis

Answer 11

• called reduction division because the chromosome number is halved from diploid 46 to haploid 23
• used for gamete formation
• happens in reproductive organs (testes & ovaries)
• 4 haploid cells are produced from 1 diploid cell
• daughter cells are genetically different to parent cells and to each other
• has an interphase stage

Question 12

meiosis steps

Answer 12

1. parent diploid cell has 46 chromosomes, 46 chromatids
2. chromosomes make identical copies of themselves: 46 chromosomes, 92 chromatids
3. homologous chromosomes pair up
4. sections of DNA get swapped (crossing over)
5. cell divides once, producing 2 haploid cells with 23 chromosomes, 46 chromatids
6. haploid cells further divide, giving 4 haploid daughter cells with 23 chromosomes, 23 chromatids

Question 13

binary fission

Answer 13

• the process by which asexual reproduction happens in bacteria
• a single organism becomes two independent organisms
• binary fission also describes the duplication of organelles in eukaryotes (eg. mitochondria)

Question 14

binary fission steps

Answer 14

1. DNA is replicated within the cell
2. DNA is separated into alternate ends of the single cell
3. the plasma membrane pinches the cell apart, and one cell becomes two
4. they become independent organisms
5. daughter cells are genetically identical if no mutations occur in the DNA when copied

Question 15

The offspring in sexual reproduction are genetically different to…

Answer 15

• their parents because they receive half of their genetic information from each parent in the gametes
• each other because the gametes produced by meiosis are genetically different from each other and it is completely random which of the gametes from each parent will then fuse at fertilisation to form the zygote.

Question 16

Importance of producing genetically different offspring

Answer 16

• so that genetic variation is maintained within a species.
• genetic variation is essential for natural selection.
• natural selection enables populations of organisms to adapt to changes in the environment. It ensures the successful continuation of a species over time.
• genetic variation within a species also helps to reduce inbreeding depression occurring

Question 17

zygote definition

Answer 17

a fertilised egg

Question 18

vesicle

Answer 18

a structure within or outside a cell, consisting of liquid or cytoplasm enclosed by a lipid bilayer which transport of materials within the plasma membrane.

Question 19

phagocytosis

Answer 19

the movement of large particles into the cell by the infolding of a region of cell membrane

Question 20

pinocytosis

Answer 20

the movement of liquid into the cell by the infolding of a region of cell membrane

Question 21

exocytosis

Answer 21

the movement of substances out of the cell by the fusing of vesicles with the cell membrane

Question 22

starch

Answer 22

animal cells do not contain starch

Question 23

active transport

Answer 23

• requires a transport protein and ATP
• the relative concentration of the materials being transported have little impact on the rate of active transport
• gases (e.g. O2 and CO2) are never actively transported

Question 24

electrochemical gradient

Answer 24

• chemical gradient: differences in the conc of substances outside vs inside the a cell (flows from high to low conc)
• electrical gradient: a +ve ion flows from +ve to -ve regions and vice versa

Question 25

tonicity

Answer 25

- hypotonic solution=has a lower concentration of solutes than another solution - hypertonic solution=has a greater concentration of solutes than another solution

Question 26

facilitated diffusion

Answer 26

- requires a transport protein | - does not require ATP

Question 27

osmosis vs diffusion

Answer 27

-osmosis must occur across a partially permeable membrane, diffusion doesn't

Question 28

the cell cycle

Answer 28

- cell growth - DNA replication - further growth occurs and the DNA is checked for replication errors - mitosis - cytokinesis - temporary cell resting period/cell stops dividing

Question 29

mitosis steps

Answer 29

- Prophase: chromosomes become visible - Metaphase: nuclear membrane breaks down, chromosomes line up along the middle of the cell - Anaphase: spindle fibres pull chromatids apart to the cell poles - Telophase: nuclei form around the groups of chromosomes at each pole - Cytokinesis: splitting of cytoplasms