Cells

Question 1

eukaryotic vs prokaryotic cells

Answer 1

• eukaryotic: complex
  they have a cell membrane, cytoplasm and their genetic material in a nucleus eg. plant and animal cells
• prokaryotic: smaller
  they have a cytoplasm, cell membrane and cell wall
  no nucleus, single DNA loop and small rings of DNA (plasmids) eg. bacteria

Question 2

plant vs animal cells

Answer 2

• animal cells have cell membrane, ribosomes, mitochondria, cytoplasm and nucleus
• plants have all this and a cell wall, (permanent) vacuole, chloroplasts

Question 3

magnification equation

Answer 3

magnification = image size/real size

Question 4

functions of organelles

Answer 4

nucleus - contains genetic material
vacuole - contains cell sap
cytoplasm - where chemical reactions take place
mitochondria - where respiration happens
chloroplasts - photosynthesis
cell wall - made of cellulose, strengthens cells
cell membrane - controls what passes in or out of the cell
ribosomes - where protein synthesis happens

Question 5

required practical - microscopy

Answer 5

1. add a drop of water to the middle of a clean slide
2. use tweezers to peel off epidermal tissue (thin layer) from the bottom of an onion
3. using tweezers, place epidermal tissue on top of the water on the slide
4. add a drop of iodine solution (a stain to highlight subcellular structures)
5. put a cover slip on top and avoid any air bubbles

Question 6

electron vs light microscopy

Answer 6

electron microscope higher magnification and resolution; powered by electrons

Question 7

what are specialised cells?

Answer 7

cells that have a particular function they carry out eg. rbc, root hair cell, sperm cell

Question 8

what are stem cells?

Answer 8

undifferentiated cells which don’t have a particular function
- they’re found in early human embryos which can differentiate into any cells or in bone marrow which only differentiate into some types of cells eg. blood cells

Question 9

what is therapeutic cloning?

Answer 9

• embryo is made to have same genetic info as patient= avoid rejection by patient’s body=replace faulty cells

Question 10

what are the risks using stem cells?

Answer 10

stem cells grown in lab=contaminated with pathogens =passed to the patient=sicker
ethical issues with embryonic stem cells

Question 11

where are stem cells found in plants?

Answer 11

meristem tissue which can differentiate into any cells throughout the plant’s life

Question 12

how are plant stem cells used?

Answer 12

• producing clones= quick+cheap
• growing crops of identical plants with desired features for farmers
• growing rare species of plants= (stop) dissaperance

Question 13

cell differentiation animals vs plants

Answer 13

• animal cell differentiate before birth
• plant cells can differentiate throughout a plant’s life

Question 14

what is binary fission?

Answer 14

a type of simple cell division that happens in bacteria
one bacteria cell splits into 2

Question 15

how often can bacteria carry out binary fission?

Answer 15

every 20 mins if they have enough nutrients and are in the correct temp

Question 16

binary fission equation

Answer 16

no.of bacteria= 2^n
n= no. of rounds of division

Question 17

how can bacteria be cultured?

Answer 17

• nutrient-broth solution
• agar gel plate

Question 18

required practical 2: aseptic technique

Answer 18

• sterilise agar gel plate and culture to avoid contamination and pathogens growing
• sterilise inoculating loop before transferring bacteria
• after transferring the bacteria, lightly secure the lid of the petri dish and store it upside down= stops pathogens in air getting in+ stops condensation
• incubate at 25°C (school lab)

Question 19

what does the nucleus contain?

Answer 19

23 pairs of chromosomes which contain a large number of genes

Question 20

cell division by mitosis

Answer 20

first stage
1. DNA replicates to form 2 copies of each chromosome
2. cell grows and copies organelles eg. mitochondria
second stage
3. one set of chromosomes is pulled to each end of the cell
4. nucleus divides
third stage
5. cytoplasm+cell membrane divide=two genetically identical cells

Question 21

what is mitosis used for?

Answer 21

• growth+development of multicellular organisms eg. animals
• repair eg. a broken bone healing
• asexual reproduction

Question 22

what is diffusion?

Answer 22

movement of molecules from a high to low concentration

Question 23

factors that affect the rate of diffusion

Answer 23

• concentration gradient - bigger= faster rate = net movement on 1 side is greater
• temp - higher=faster=particles have more Ek=more movement+more often
• surface area - large=faster=more particles can pass at once

Question 24

why do multicellular organisms have exchange surfaces eg. lungs?

Answer 24

they have a small sa:v ratio= not enough substances can diffuse from surface to supply their volume

Question 25

how are exchange surface adapted?

Answer 25

• thin membrane=short diffusion pathway
• large sa:v ratio=lots of substances can diffuse at once
• efficient blood supply
• gas exchange surfaces eg. alveoli= ventilated

Question 26

what is osmosis?

Answer 26

movement of water particles from a dilute to concentrated solution through a partially permeable membrane

Question 27

required practical 3: potatoes+osmosis

Answer 27

• cut 3 potato cubes
• measure the length using a ruler
• use a balance to weigh the cubes
• measure 10 cm3 of a 1 M sugar solution, 0.5 M sugar and one in distilled water
• add a cube in each solution
• leave the potato cylinders in the boiling tubes overnight in the test tube rack
• tap them dry to remove any excess water
• re-measure the length and mass of each cylinder
• work out the percentage change in mass
• plot a graph with the results

Question 28

what is active transport?

Answer 28

movement of particles against their concentration gradient using energy from respiration