Paper one: B1 Cells

Question 1

Animal cell structure

Answer 1

• Semi permeable membrane: controls what enters and leaves
• DNA in a nucleus
• mitochondria (where respiration occurs)
• cytoplasm (where most chemical reactions occur)
• ribosomes (where proteins are synthesised)(assembled)

Question 2

Plant cell structure

Answer 2

• semi permeable membrane controlling what enters and leaves
• cellulose cell wall to provide a rigid structure
• cytoplasm (liquid in which chemical reactions take place)
• mitochondria (respiration)
• ribosomes (protein synthesis)
• chloroplasts, which contain chlorophyll, required for photosynthesis
• permanent vacuole which stores sap

Question 3

Binary fission

Answer 3

bacteria multiple by simple cell division: binary fission
Bacteria reproduce by binary fission: they divide once every 20 minutes, as long as they have enough nutrients and the temp is suitable. Meaning, Every 10 minutes, the number doubles.

Question 4

REQUIRED PRACTICAL: making cultures with aseptic techniques

Answer 4

1. lift lid of petri dish towards flame (to sterilise air by moving microbes away/ killing them)
2. Place drop of culture on agar and spread evenly
3. put drops or discs of antibiotics on culture if needed
4. Tape the lid but not all the way around to allow aerobic respiration
5. incubate at 25*
6. measure size of cultures OR area with no bacteria using pi x r squared

Question 5

Diploid cells

Answer 5

a cell (such as human) with 23 PAIRS of chromosomes (46 in total)

Question 6

haploid cells

Answer 6

Gametes (egg/sperm cells) with just 23 chromosomes

Question 7

MITOSIS

Answer 7

carried out by diploid cells
1. Dna replicates to form two copies of each chromosome. Cell also grows and copies it’s internal structures such as mitochondria and ribosomes.
2. mitosis takes place: chromosomes align in the centre of the cell, and are pulled to opposite ends of the cell. The nucleus also divides.
3. Cytoplasm and cell membrane divide to form two identical daughter cells , with two pairs of chromosomes

Question 8

Order of magnitude

Answer 8

calculated by the amount of zeros

Question 9

mitichondria

Answer 9

aerobic respiration takes place

Question 10

Diffusion

Answer 10

movement of particles from an area of high concentration to that of a low concentration (down the concentration gradient)

requires no energy (passive)

Question 11

Osmosis

Answer 11

the diffusion of water across a semi permeable membrane to balance the concentrations of solution inside and outside of a cell.

Question 12

Rate of osmosis can be increased by increasing:

Answer 12

• difference in concentrations
• surface area
  temperature

Question 13

REQUIRED PRACTICAL: Osmosis

Answer 13

1. cut equal sized cylinders from a potato
2. weigh and place in test tubes with varying concentrations of sugar solutions
3. after a day, remove them, damp the excess water off the surface, and re-weigh.
4. calculate percentage change in mass by doing (final mass subtract initial mass)
   ———————————————x 100
   initial mass

If it’s later than before, it’s a negative change in mass

Question 14

specialised cells

Answer 14

cells with adaptations wich help them carry out their particular function
most animal cells are specialised
when they become specialised, it’s called differentiation.

Question 15

ANIMAL CELL SPECIALISATION: sperm cells

Answer 15

• long tail to allow to swim to ovum
• streamlined to make swimming easier and faster
• packed full of mitochondria, providing energy needed for swimming
• contain enzymes, allowing them to digest the outer layer of the ovum

Question 16

ANIMAL CELL SPECIALISATION: Nerve cell

Answer 16

• Myelin insulates the axon and speeds up the transmission of nerve impulses
• synapses are junctions which allow the impulse to pass from one nerve cell to another
• dendrites increase the surface area so the nerve cells can connect more easily

Question 17

ANIMAL CELL SPECIALISATION: Muscle cell

Answer 17

• contain protein fibres which can change their length (allowing them to contract, and the protein fibres shorten. decreasing length of cell)
• packed full of mitochondria to provide energy for muscle contraction

Question 18

PLANT CELL SPECIALISATION: Root hair cell

Answer 18

• hairs: these increase the surface area, so it can absorb water and dissolved minerals effectively
• ## do not contain chloroplasts because they are underground, and do not need to undergo photosynthesis

Question 19

PLANT CELL SPECIALISATION: Xylem cells

Answer 19

• very thick walls containing lignin- provides support for the plant
• the end walls between the cells have broken down: the cells can now form a king tube divested and dissolved minerals can flow easily
• no nucleus, cytoplasm, vacuole or chloroplasts: no internal structures at all, making it easier for water and minerals to flow

Question 20

PLANT CELL SPECIALISATION: Phloem cells

Answer 20

• Phloem vessel cells and sieve plates allow dissolved sugars to move through the cell interior
• mitochondria in the companion cell provide energy to the phloem vessel cell

Question 21

Optical microscopes

Answer 21

• stage: where the microscope slide is placed. has clips to hold the slide in place.
• lamp: found below the stage. light from the lamp passes up through the microscope slide
• lenses: above the stage, a set of lenses, called objective lenses. 3 different lenses, with a magnification of 4x 10x and 40x
• eyepiece: at the top of microscope. where we look through. Contains the eyepiece lens which has a magnification of 10x
• coarse focusing dial:
• fine focussing dial:

Question 22

REQUIRED PRACTICAL: Microscopes

Answer 22

1. place slide onto the stage and use clips to hold in place
2. select the lowest power objective lens, usually 4x
3. position the objective lens so it almost touched the microscope slide: do this using the coarse focussing dial, turning slowly
4. LOOK AT THE MICROSCOPE FROM THE SIDR WHILST ADJUSTING THE POSITION OF THE OBJECTIVE LENS : when it almost touched the slide, stop turning the dial. Looking through the eyepiece whilst adjusting, creates a risk of damaging the slide.
5. now look down through the eyepiece
6. slowly turn the coarse focussing dial: this increases the distance between the objective lens and the slide. do this until cells come into focus
7. on any drawing, include the magnification scale: place a clear plastic ruler over the stage, measure the diameter of the field of view in millimetres. show this on drawing using a scale bar. Write the magnification beside it.
8. use fine focussing dial to bring the cells into a clear focus

Question 23

EQUATION: total magnification

Answer 23

eyepiece lens magnification x objective lens magnification

Question 24

EQUATION: Number of bacteria

Answer 24

number of bacteria: 2 to the power of n
where n is the number of rounds of division

Question 25

What do chromosomes carry

Answer 25

in humans, hundreds of genes

Question 26

Functions of Mitosis

Answer 26

1. essential for growth and development of multicellular organisms (plants and animals)
2. mitosis takes place when an organism repairs itself (eg when a broken bone heals)
3. happens during asexual reproduction