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GCSE BIOLOGY PAPER 2 > B6 > Flashcards

B6 Flashcards

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1
Q

What is the difference between asexual and sexual reproduction?

A

sexual reproduction - the mixing of genetic information which leads to variety in offspring. (two parents)

Asexual reproduction - involves only 1 parent and no fusion of gametes

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2
Q

What are the male and female gametes in humans?

A

sperm and egg cells

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3
Q

What are the male and female gametes in flowering plants?

A

pollen and egg cells

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4
Q

What does mitosis produce?

A

Two genetically identical daughter cells

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5
Q

True or false: Asexual reproduction involves meiosis?

A

false: asexual reproduction only involves mitosis

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6
Q

Why do cells in reproductive organs divide by meiosis?

A

to form gametes

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7
Q

Give an outline of what happens during meiosis

A

Meiosis halves the number of chromosomes in gametes and fertilisation restores the full number of chromosomes

  • copies of genetic information are made
  • the cell divides twice to form four gametes, each with a single set of chromosomes
  • all gametes are genetically different from each other.
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8
Q

What do gametes do to restore the number of chromosomes?

A

they join at fertilisation and the new cell divides by mitosis

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9
Q

What is DNA?

A

a polymer made up of two strands of nucleotides which form a double helix structure

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10
Q

What is a gene?

A

a gene is a small section of DNA on a chromosome and each gene codes for a particular sequence of amino acids (make a specific protein)

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11
Q

What is the genome?

A

The entire genetic material of that organism

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12
Q

Why is understanding the human genome important?

A
  • to search for genes linked to different types of disease
  • understanding and treatment of inherited disorders
  • understanding and tracing human migration patterns from the past
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13
Q

What is DNA? (structure)

A

a polymer made from four different nucleotides
• each nucleotide consists of a common sugar and phosphate group with 1 of 4 bases attached to the sugar

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14
Q

What are the four bases? (and their complementary base pairings)

A

A and T

G and C

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15
Q

Where are protein synthesised?

A

on ribosomes (according to a template)

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16
Q

Explain the process of protein synthesis

A

Transcription and Translation

  • Transcription: process of taking a single piece of DNA and copying it into a structure known as mRNA
  • Translation: process of taking the mRNA strand and using it to produce a protein
17
Q

Explain transcription

A
  1. Starts with an enzyme called RNA polymerase which binds to the DNA just before the gene starts
  2. The two strands of DNA separate so that all the strands of their bases are exposed.
  3. The mRNA bases are always complementary to the DNA bases
  4. Once the RNA polymerase has finished forming the mRNA strand it detaches from the DNA and the DNA strands are able to close back up
  5. The mRNA is free to leave the nucleus and head to the ribosome
  6. Template strand= the strand of DNA which the RNA polymerase moved across
18
Q

Explain translation

A
  1. each codon codes for a different amino acid (our body uses 20 amino acids to form proteins)
  2. The mRNA and the ribosome bind together and the ribosome adds one amino acid at a time which is brought by tRNA (transfer RNA)
  3. tRNA have the amino acid and the top and an anti-codon (sequence of 3 bases which are complentary to the mRNA) on the bottom which ensures the correct tRNA is attracted each time
  4. The correct amino acids are brought to the ribosome in the correct order so they can be joined together to build up a chain of amino acids
  5. Once this process is complete, the amino acid chain is able to detach from the ribosome and fold up on itself to form a protein
19
Q

What are the differences between mRNA and DNA?

A
  • much shorter than DNA
  • only a single strand rather than two in DNA
  • instead of the T base (Thymine) mRNA has a U base (Uracil)
20
Q

What do non-coding parts of DNA do?

A

they can switch genes on and off, so variations in these areas of DNA may affect how genes are expressed

21
Q

What is a mutation? What can increase the risk?

A

a change in the DNA base sequence and these happen spontaneously in our cells

  • the risk of mutations is increased by carcinogens
  • certain types of radiation (e.g. gamma rays)
22
Q

What are the three types of mutations?

A
  1. insertion: an extra base is inserted into the base sequence somewhere (worse than substitution)
  2. deletion; one of the bases is deleted from the sequence
  3. substitution: when one of the bases is changed for another random base
23
Q

What could a mutation do to an enzyme?

A

change the shape of the active site so it would no longer be complementary to the specific substrate

24
Q

What is an allele?

A

a different form of a gene

25
Q

Give examples of characteristics which are controlled by a single gene

A
  • fur colour in mice
  • red-green colour blindness
26
Q

What is a dominant allele?

A

The allele which is always expressed, whenever it is present

27
Q

What is a recessive allele?

A

an allele which is only expressed if two copies are present

28
Q

Explain the difference between homozygous and heterozygous

A
  • If the two alleles present are the same the organism is homozygous
  • If the alleles are different they are heterozygous
29
Q

Define genotype

A

an individual’s collection of genes

30
Q

Define phenotype

A

an individual’s physical characteristics (observable traits)

31
Q

What is polydactyly?

A

An inherited disorder which involves having extra fingers or toes and is caused by a dominant allele

32
Q

What is cystic fibrosis?

A

A disorder of cell membranes which causes thick mucus to be built up in the lungs and digestive system, caused by two recessive allele

GCSE BIOLOGY PAPER 2 (3 decks)

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