U2 BIO IAL Edexcel CAQ/mock/mistakes

Describe how you would prepare cells in order to observe mitosis

(4 marks)

-take sample of root tip

- add HCL acid to root tip (to breakdown lamella/celloluse)

- add stain such as toluidine blue/methy blue and warm to make stain more visible

- Use a mounted needle to break open the root tip

- then gently squash under coverslip

(squash so that cells are seperated and mitosis is visible)

second point is wrong as (homologous) chromsome pairs of chromsome separate during meiosis, not mitosis.

C

Why does reduced gene expression due to disease cause less growth in plant (2marks)

• reduced gene expression means fewer proteins and enzymes are formed

• these are needed for growth and cell division, so plant growth is reduced
  
  reduced gene expression → fewer proteins/enzymes → less growth/cell division

difference between fungal cell and cell from root of plant (2 marks)

- fungal cell will have glycogen granule but root cell will have starch granule

- fungal cell has cell wall made from chitin whereas root cell wall is from cellulose

Suggest why the number and size of the Golgi apparatus change during the cell cycle (4marks)

• mitosis produces two daughter cells from one cell

• therefore the size and number of Golgi apparatus increase during interphase/G1

• so enough organelles/cell contents are present for both daughter cells after mitosis

• increased protein synthesis/modification occurs, requiring more Golgi apparatus

(before mitosis cells grow + make proteins → Golgi increases so both daughter cells receive enough organelles)

Explain why alleles b and e are more likely to be inherited together than alleles A and e.

- alleles b and e are on the same chromosome and closest together

- therefore they are less likely to be seperated in crossing over

Describe how independent assortment and how crossing leads to further genetic variation (4marks)

- in independednt assortment homologous chromosomes randomly line up in the middle

- each daughter cell gets a random mix of maternal and paternal chromosomes thus, new combinations of allele form

- in crossing over non sister chromatids overlap and exchange segments

- new recombinant allele is formed increasing genetic diversity

which of the following are present in plant leaf cells:

amyloplast

chloroplast

golgi apparatus

plasmodesmata

answer: ALL of them are present

state 3 similarities between golgi and smooth ER

- both have stacks of flattened and curved cistarnae

- both have single membrane

- both have no ribosome

Suggest reasons that two organisms are classified into same genus but different species (such as blue whale and fin whale) [3marks]

- they have similar behavioral and anatomical features so they are same genus

(- they have similarities in molecular phylogeny)

- they are different species since they cannot interbreed and produce fertile offsrping

- rather they produce infertile offsrping

(Interbreeding refers to mating between different species, subspecies, or distinct populations to produce hybrids)

Explain how seed banks work and why they are importnat/advantageos (5marks)

- seeds are collected from various places and then cleaned, sterilised and dried

- then seeds are stored in dry, frozen and air tight containers

- the seeds are regulary cheked for viability by using x-ray

- seed banks require less space (than storing fully grown plants) and are cheaper

- seeds in seed banks are well protected from diseases and natural disasters

- they prevent species from going extinct

Sisal is made from schelerenchyma fibres and nylon is a synthetic fibre. Both are used to make rope.

Suggst 3 advantages of using sisal rather than nylon to make rope

- sisal is biodegradeable & renewable as its made from plant fibre schelerenchyma

- sisal is cheaper

- sisal does not need fossil fuel

give 4 similairties between xylem and shcelernchyma

- both are dead cells

- both have very thick cell wall

- both contain lignin

- both provide mechanical support to plant

Describe the structure of a cellulose microfibril

(5marks)

- cellulose is an unbranched polymer

- which consists of beta glucose joined together by 1,4 glycosidic bonds

- every alternate beta glucose is inverted

- Cellulose molecules are held together by many H- bonds to form microfibrils

(- H-bond between adjacent OH groups)

- there are layers of microfibrils which are arranged in a mesh/ crisscross pattern

State what is meant by the following terms:

- magnification (1mark)

- resolution (1mark)

- magnification = how much larger an object appears in an image compared to actual size

- resolution = ability to distinguish two points which are close together

(in a speciment, allowing structures to be distinguished)

Explain how enzymes from cortical granules prevent polyspermy

(3marks)

- (the enzymes are involved in cortical reaction where)

cortical granules fuse with cell membrane and release the enzmyes

- thus causes the zona pellucida to harden and thicken

- hence acrosin(or hydrolytic enzymes from sperm) can no longer digest the zona pellucida, preventing polyspermy

give 3 reasons how eductation could help conserve an endagered species of trees like the baobab

(3marks)

- educates people to reduce deforestation / avoid cutting trees

- educates people to plant more baobab trees

- teaches methods such as artificial pollination to increase reproduction

(& thus increase population of baobab trees)

state the directions of xylem and phloem water transport

(2marks)

- xylem transports water upwards ONLY (via transpiration pull)

- phloem can transport water both up and down

(via translocation, active transport)

Describe what happens to DNA during interphase

(3marks)

- DNA is uncondensed

[ uncondensed form of DNA = chromatin allows for better transcription and replication ]

- DNA is replicated (S phase)

- DNA undergoes transcription (G1 and G2)

[btw protein synthesis actually occurs in interphase]

( condensed form of DNA = chromosome)

REJECT organ synthesis even tho it's right, Q. specefically wants DNA

A disease causes a father's chromosome 13 to have error in meiosis.

Explain how this error in meiosis can lead to the production of a zygote with 3 copies of chromosome 13 (trisomy 13).

(4marks)

- normally centromere of chromosomes divide in

anaphase-II of meiosis, but here due to error it doesn't

- so the sister chromatids of chromosome 13 are not seperated (and pulled to the same pole)

- hence sperm nuclues has 2 copies of chromosome 13

(normally it is 1 copy)

- as a result, when sperm nuclues fuses with egg cell nuclues the zygote formed has 3 copies of chromosome 13

[2 from father & 1 from mother]

give 2 advantages of slimy capsule of bacteria

(2marks)

- prevents bacteria from drying out (or dehydration)

- protects it from antibiotics and digestive enzymes

Two groups are tested for a drug. 1000 patients used in each group to see if swelling caused by skin bactiria reduced after using drugs

Group A: (Initial swell) 2.18 --> 1.77 (after 10days)

Group B: (Initial swell) 2.04 --> 1.42

Comment on the resulsts of this investigation

(4marks)

- swelling reduces for BOTH groups overtime

[ obvious statement but its still 1 mark]

- treatment for group B is more effective

(has higher antimicrobial effect)

- as B had greater overall reduction in swelling than A

[ diff in A = 2.18 - 1.77 = 0.41 , Diff in B = 2.04 - 1.42 = 0.72

ALWAYS CALCULATE to see which acc is more effective]

- small sample size so less validity

(OR no mention of other factors such as body mass

OR no S.D so no indication of variation in data )

define:
chromatid
Chromatin

• Chromatid is one of the two DNA molecules that make up a chromosome
  

• formed during S Phase of interphase when DNA replicates
  
  
  - chromatin is the loose, non-condensed version of chromosomes

state 2 functions of parenchyma and collenchyma (4 marks)

parenchyma:

- photosynthesis

- stores starch

collenchyma:

- provides mechanical support

- gives flexibility to plant

what is xylem cell wall made of?

celloluse AND lignin

Describe how plants from these rainforests could be tested for their antimicrobial properties (5marks)

- test different parts of the plant such as root and leaves

- crush the plant material to produce an extract

- add bacteria to agar

- soak discs in the extract (or add extract to wells) and place onto the agar

and keep at 20–35°C for 1–7 days
- use sterile equipments

- then measure the area of zone of inhibition and repeat the experiment to calculate the mean

Describe one method that could be used to conserve endangered plant species
(2 marks)

• store seeds

• in seed banks