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Biology Unit 2 > B2.7 + 8 Cell Division and Inheritance + Speciation > Flashcards

B2.7 + 8 Cell Division and Inheritance + Speciation Flashcards

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1
Q

Where are pairs of chromosomes found?

A

In the nucleus

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2
Q

What is a ‘gene’?

A

A section of DNA containing instructions to make a specific protein

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3
Q

How do cells code for proteins?

A
  • Each gene codes for a particular combination and order of amino acids which make a specific protein.
  • DNA also determines what protein the cell produces which determines what type of cell it is e.g haemoglobin - red blood cell
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4
Q

Name 2 exceptions to the rule of everyone having unique DNA

A
  • Identical twins

- Clones

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5
Q

Name 2 uses of DNA fingerprinting

A
  • Forensic science: DNA taken from a crime scene is compared with suspect’s DNA
  • Paternity testing
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6
Q

What do chromosomes contain?

A

Genetic information

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7
Q

What are two uses of mitosis?

A
  • Growth

- To produce replacement cells for damaged ones

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8
Q

How many chromosomes do diploid cells have?

A

46 (23 pairs)

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9
Q

How many chromosomes do haploid cells have?

A

23 (no pairs)

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10
Q

What are the only haploid cells in the body?

A

Gametes

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11
Q

What are the reproductive organs of a male?

A

The testes

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12
Q

What are the reproductive organs of a female?

A

The ovaries

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13
Q

What is meiosis?

A

A type of cell division producing gametes, cells with half the number of normal chromosomes

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14
Q

What is mitosis?

A

A type of cell division when a cell reproduces itself by splitting to form two identical clones

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15
Q

Why do gametes only have 1/2 the number of chromosomes?

A

So at fertilisation a diploid number is restored to the fertilised cell

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16
Q

Explain the process of mitosis.

A
  • Chromosomes are duplicated
  • DNA forms X-shaped chromosomes with each ‘arm’ being an exact duplicate of the other
  • They line up at the centre of the cell and attach to spindle fibres
  • These fibres pull them apart and two arms of each chromosome goes to opposite ends of the cell
  • Membranes form around each of the sets of chromosomes (now the new nuclei of two cells)
  • They cytoplasm divides in half (Cleavage)
  • Two new genetically identical cells are formed
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17
Q

What type of reproduction uses mitosis?

A

Asexual reproduction

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18
Q

Name an example of an organism which reproduces asexually.

A

Strawberry plants forming runners

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19
Q

Explain the process of meiosis.

A
  • Chromosomes duplicate
  • In the first division, the chromosomes line up at the centre of the cell
  • Pairs are pulled apart to the opposite ends of the cell, so each new cell only has one copy of each chromosome
  • Some of the first cell’s and some of the second cell’s chromosomes go into each new cell
  • In the second division, the chromosomes line up again in the centre of the cell, the arms are then pulled apart. (like mitosis)
  • Four new gametes are formed with 1/2 the number of normal chromosomes
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20
Q

What happens after fertilisation?

A

The cell grows by repeatedly dividing with mitosis

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21
Q

Define differentiation

A

Becoming specialised for a particular function and being unable to change into other types of cell.

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22
Q

What is differentiation caused by?

A

Genes switching on and off

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23
Q

What is the difference between animal cells and plant cells in differentiation?

A

Animal cells only differentiate at an early stage once and then lose the ability whereas plant cells retain it throughout their life.

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24
Q

How is plant cell differentiation used?

A

Huge numbers of identical plant clones are grown from one tiny piece of tissue.

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25
Q

What is a stem cell?

A

Undifferentiated cells which can develop into any different type.

26
Q

What are embryonic stem cells?

A

Stem cells extracted from very early human embryos that can differentiate into any type of cell.

27
Q

How do researchers control embryonic stem cell differentiation?

A

By changing the environment they’re growing in.

28
Q

What conditions/diseases could embryonic stem cells cure?

A
  • Heart disease (beating heart muscle)
  • Diabetes (insulin producing cells)
  • Paralysis (new nerve cells)
29
Q

What are adult stem cells?

A

Stem cells found in the bone marrow that can only differentiate into red and white blood cells

30
Q

Name a condition adult stem cells can treat

A
  • Sickle cell anaemia (new blood cells)
31
Q

Why are people against stem cell research?

A
  • Human embryos are potential life
  • Embryos have no say
  • Scientists should use other sources of stem cells rather than embryos
32
Q

What is an ‘allele’?

A

Different versions of the same gene which determine different characteristics.

33
Q

What are the offspring of asexual reproduction like?

A

They have the same alleles as their parents

34
Q

What are the offspring of sexual reproduction like?

A

They have variation, a combination of alleles from both their parents.

35
Q

What pair of chromosomes determines the male sex?

A

XY

36
Q

What pair of chromosomes determines the female sex?

A

XX

37
Q

Define ‘dominant allele’

A

An allele that produces the same phenotype whether its paired allele is identical or different.

38
Q

Define ‘recessive allele’

A

An allele that only produces the same phenotype if its paired allele is identical.

39
Q

Define ‘homozygous’

A

An individual which two identical alleles for a characteristic

40
Q

Define ‘heterozygous’

A

An individual which two different alleles for a characteristic

41
Q

Define ‘genotype’

A

The genetic make up of an individual regarding a particular characteristic

42
Q

Define ‘phenotype’

A

The physical appearance of an individual regarding a particular characteristic

43
Q

What is the shape of a DNA molecule?

A

A double helix

44
Q

Who was Mendel?

A

A monk who discovered the laws of inheritance by breeding pea plants.

45
Q

Why was Mendel not believed at the time about his work?

A
  • DNA/genes hadn’t been discovered

- He was not a reputable scientist

46
Q

What is poldyactyly?

A

A genetic disorder caused by a dominant allele where a baby is born with extra toes or fingers.

47
Q

What is cystic fibrosis?

A

A genetic disorder caused by a recessive allele where the body produces excess mucus in the air passages and pancreas.

48
Q

How are embryos screened for genetic disorders?

A
  • During IVF, before implanting an embryo, a cell is removed from each one.
  • Their genes are analysed
  • Embryos with ‘healthy’ alleles are implanted and those without are destroyed.
49
Q

What are the arguments for embryonic screening?

A
  • It will stop people suffering
  • Treating disorders costs taxpayers money
  • During IVF most of the embryos are destroyed anyway
  • There are laws in place to stop it going too far (e.g not allowing sex selection)
50
Q

What are the arguments against embryonic screening?

A
  • Expensive
  • Can lead to designer babies
  • Implies people with genetic disorders are ‘undesirable’
  • Rejected embryos are destroyed - they had potential for human life.
51
Q

What are fossils?

A

The remains of organisms from many years ago found in rocks.

52
Q

Name 3 ways fossils can be formed.

A
  • Gradual replacement by minerals
  • From casts and impressions
  • Preservation.
53
Q

Describe how gradual replacement by minerals produces fossils.

A
  • Teeth, shells and bones don’t decay easily
  • They are eventually replaced by minerals forming a rock like substance shaped like the original part
  • The surrounding sediments also turn to rock but the fossil stays distinct
54
Q

Describe how casts and impressions produce fossils.

A
  • An organism is buried in a soft material (e.g clay)

- The clay later hardens around it and the organism decays leaving a cast around itself.

55
Q

Give examples of fossils that come from impressions (3)

A
  • An animal’s burrow
  • Plant’s roots
  • Footprints
56
Q

Describe where and how preservation produces fossils.

A
  • In amber and tar pits there’s no oxygen/moisture so decomposers don’t survive.
  • In glaciers it’s too cold for decomposers to work
  • In peat bogs it is too acidic
57
Q

What are fossils useful for?

A

Finding out how living things evolved

58
Q

Why is the fossil record incomplete?

A
  • Some are yet to be discovered
  • Fossilisation is rare
  • Many fossils in rocks have been destroyed due to geological activity
  • Many early organisms were soft bodied and soft tissue decays
59
Q

What are 6 causes of extinction?

A
  • The environment changes too quickly
  • A new predator kills them all
  • A new disease kills them all
  • They can’t compete with another species for food
  • A catastrophic event kills them all
  • A new species develops
60
Q

Define ‘speciation’

A

The development of a new species, when populations of the same species become so different they can no longer breed fertile offspring

61
Q

Define ‘species’

A

A group of similar organisms that can reproduce to give fertile offspring

62
Q

Describe the process of speciation

A
  • Any population contains genetic variety - they have a wide range of alleles that control their characteristics
  • if one population becomes isolated from the other, the conditions they are living in are likely to be different
  • Natural selection will therefore occur differently in each group and the alleles selected that control the characteristics which help an organism survive will be different
  • Eventually the two populations will have changed so much over time that they can’t interbreed successfully

Biology Unit 2 (5 decks)

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