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IGCSE Biology > Topic 6 (mini test: units 17-18) > Flashcards

Topic 6 (mini test: units 17-18) Flashcards

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1
Q

What are chromosones?

A

Made of DNA,
which contains genetic information in the form
of genes.

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2
Q

What is a gene?

A

A length of DNA that codes for a protein.

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3
Q

What is an allele?

A

An alternative form of a gene/variant gene.

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4
Q

What do the base sequences in DNA determine?

A

The sequence of amino acids used to
make a specific protein.

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5
Q

What do different sequences of amino acids do?

A

Give shapes to different shaped protein molecules.

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6
Q

How does the DNA control cell function?

A

Controlling the production of proteins, including
enzymes, membrane carriers and receptors for
neurotransmitters.

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7
Q

How is a protein made?

A
  • the gene coding for the protein remains in
    the nucleus
  • messenger RNA (mRNA) is a copy of a gene
  • mRNA molecules are made in the nucleus
    and move to the cytoplasm
  • the mRNA passes through ribosomes
  • the ribosome assembles amino acids into
    protein molecules
  • the specific sequence of amino acids is
    determined by the sequence of bases in the
    mRNA
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8
Q

How is DNA copied?

A

Transcription, translation.

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9
Q

Most body cells in an organism
contain the same genes but why are only some expressed?

A

Many genes in a
particular cell are not expressed because the cell
only makes the specific proteins it needs.

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10
Q

What is a haploid nucleas?

A

A nucleus containing a single set of chromosomes.

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11
Q

What is a diploid nucleas?

A

A nucleus containing two sets of chromosomes.

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12
Q

What is in a diploid cell?

A

There is a pair of each
type of chromosome and in a human diploid cell
there are 23 pairs.

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13
Q

What is mitosis?

A

Nuclear division giving rise to genetically identical cells.

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14
Q

What is the role of mitosis?

A

Growth, repair of
damaged tissues, replacement of cells and
asexual reproduction.

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15
Q

What occurs before mitosis?

A

Exact replication of chromosomes occurs before mitosis.

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16
Q

What happens during mitosis?

A

The copies of
chromosomes separate, maintaining the
chromosome number in each daughter cell.

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17
Q

What are stem cells?

A

Unspecialized cells that
divide by mitosis to produce daughter cells that can become specialized for specific function.

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18
Q

What is meiosis used for?

A

Involved in the production of gametes

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19
Q

What is meiosis?

A

Reduction division in which
the chromosome number is halved from diploid
to haploid resulting in genetically different cells.

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20
Q

What is inheritance?

A

The transmission
of genetic information from generation to
generation.

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21
Q

What is a genotype?

A

The genetic make-up of an
organism and in terms of the alleles present.

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22
Q

What is a phenotype?

A

The observable features of
an organism.

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23
Q

What does homozygous mean?

A

Having two identical
alleles of a particular gene.

24
Q

What will happen when two homozygous individuals breed with each other?

A

Pure breeding.

25
Q

What does heterozygous mean?

A

Having two different
alleles of a particular gene.

26
Q

Can heterozygous individuals pure breed?

A

No.

27
Q

What is a dominant allele?

A

An allele that is
expressed if it is present in the genotype.

28
Q

What is a recessive allele?

A

An allele that is only
expressed when there is no dominant allele of
the gene present in the genotype.

29
Q

What is codominance?

A

A situation in
which both alleles in heterozygous organisms
contribute to the phenotype.

30
Q

What is a sex-linked characteristic?

A

A feature
in which the gene responsible is located on
a sex chromosome and that this makes the
characteristic more common in one sex than in
the other

31
Q

What is an example of a sex-linked trait?

A

Red-green colour blindness

32
Q

What is variation?

A

Differences between
individuals of the same species

33
Q

What is continuous variation?

A

Results in a range
of phenotypes between two extremes; examples
include body length and body mass

34
Q

What is discontinuous variation?

A

Results
in a limited number of phenotypes with no
intermediates; examples include ABO blood
groups, seed shape in peas and seed colour in
peas

35
Q

What is discontinuous variation usually caused by?

A

Genes.

36
Q

What is continuous variation caused by?

A

Environmental and genetic

37
Q

What is a mutation?

A

A random change in the base sequence of DNA.

38
Q

How do mutations occur?

A

The way in which new alleles are formed.

39
Q

How does genetic variation occur in populations?

A

Mutation, meiosis, random mating/fertilisation

40
Q

What are things that can increase the rate of mutation?

A

Ionizing radiation and some chemicals

41
Q

What is an adaptive feature?

A

An inherited feature that helps an organism to survive and reproduce in its environment

42
Q

What are hydrophytes?

A

Plants adapted to live in extremely wet conditions

43
Q

What are 3 common adaptations of hydrophytes?

A
  • Large air spaces in leaves (flotation, keep leaf close to surface of water for more light exposure - photosynthesis)
  • Small roots (extract nutrients from the water through tissues, water in excess)
  • Stomata usually open all the time - found on upper epidermis of leaf (allows easier gaseous exchange)
44
Q

What are xerophytes?

A

Plants adapted to live in extremely dry conditions

45
Q

6 Common adaptations for xerophytes:

A
  • Thick waxy cuticle (reduces water loss)
  • Sunken stomata
  • Leaf rolled with stomata inside and inner surface covered with hairs
  • Small leaves
  • Extensive shallow roots
  • Thickened leaves/stems
46
Q

How does the thick waxy cuticle help xerophytes?

A

It cuts down water loss by
- acting as a barrier to evaporation
- shiny surface reflects heat, therefore lowering the temperature of the water

47
Q

How does sunken stomata help xerophytes?

A

Stomata may be sunk in pits in the epidermis; moist air trapped here lengthens the diffusion pathway, reducing evaporation rate

48
Q

How does the leaf rolled with stomata inside and an inner surface covered with hairs help xerophytes?

A

Traps moist air, prevents air movement across stomata which reduces transpiration

49
Q

How do small leaves help xerophytes?

A

Small, needle-shaped leaves reduce the surface area (the evaporating surface)

50
Q

How do extensive shallow roots help xerophytes?

A

Allow for quick absorption of large quantities of water when it rains

51
Q

How do thickened leaves/stems help xerophytes?

A

Contain cells that store water

52
Q

What is adaptation?

A

The process resulting from natural selection, by which populations become more suited to their environment over many generations

53
Q

What is natural selection?

A

Natural selection allows for genetic variation within populations - allowing the one with traits most compatible to the environment to have a higher probability of surviving. These organisms have a greater chance of reproduction by
individuals that are better adapted to the environment than others. These individuals pass their alleles onto the next generation

54
Q

What is selective breeding?

A

The selection by humans of individuals with desirable features and crossing them to produce the next generation. The selection of offspring showing the most desirable features and repeat the process.

55
Q

What is an example of natural selection?

A

The development of strains of antibiotic resistant bacteria

56
Q

Why is selective breeding by artificial selection is carried out over many generations?

A

To improve crop plants and domesticated animals

57
Q

What are the differences between natural and artificial selection?

A
  • Natural selection occurs naturally (artificial only occurs when humans intervene)
  • Natural results in development of populations with features that are better adapted to their environment and survival (artificial results in development of populations with features that are useful to humans and not necessarily to survival)
  • Natural selection usually takes a long time to occur ( artificial takes less time to occur as only individuals with the desired features are allowed to reproduce)

IGCSE Biology (10 decks)

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