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Biology A-LEVEL > Topic 2- 2.4 Meiosis And Sexual Reproduction > Flashcards

Topic 2- 2.4 Meiosis And Sexual Reproduction Flashcards

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1
Q

What is a diploid cell?

A

It signifies a cell which contains two full set of chromosomes. Referred to as (2n)

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2
Q

What is a haploid cell?

A

It signifies a cell with a nucleus that only contains one full set of chromosomes. Referred to as (n)

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3
Q

What is a zygote?

A

Is the cell formed when the two haploid gametes fuse at fertilisation

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4
Q

Describe fertilisation.

A

Is the fusing of the haploid nuclei of the two haploid gametes to form. Diploid zygote in sexual reproduction (2n)

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5
Q

What is polypoidy?

A

Is when a cell or an organism has more than two or more sets of chromosomes

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6
Q

What is spermatozoa?

A

Are the haploid male gametes in animals

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7
Q

What Is Ova?

A

The female haploid gamete found in animals

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8
Q

What are homologous chromosomes?

A

Describe a set of one maternal and one paternal chromosomes that pair up during meiosis cell division.

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9
Q

What does it mean for chromosomes to cross over?

A

Is the process by which large multi enzyme complexes cut and rejoin parts of the maternal and paternal chromosomes at the end of prophase 1

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10
Q

What is independent assortment?

A

Is the process by which chromosomes derived from the female and male parent are distributed into the gametes at random

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11
Q

What are the chaismata?

A

The points where the chromatids break during recombination

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12
Q

What is translocation?

A

Is a mutation in which part of one chromosome breaks off and rejoins to another completely different chromosome. It maybe balanced, if two chromosomes swap. It may be unbalanced if a piece breaks off one chromosome and joins another

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13
Q

What sex chromosomes do females have?

A

XX

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14
Q

What sex chromosomes do males Have?

A

XY

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15
Q

What is non-disjunction?

A

Is the process that occurs when members of a pair of chromosomes fail to separate during the reduction division of meiosis, resulting in one gamete with two copies of a chromosome and one gamete containing no copies of that chromosome

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16
Q

What is monosomy?

A

Is when only one member of a pair of chromosomes is present in a cell

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17
Q

What is polysomy?

A

Is when cell contains three or more rather than two chronometer of a particular type

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18
Q

What is aneuploidy?

A

Is when a cell contains too few or too many chromosomes

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19
Q

What is the mutation rate?

A

Is the rate at which mutation naturally occurs

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20
Q

What is a mutagen?

A

Are chemicals known to increase the rate of mutation

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21
Q

What causes Down’s syndrome?

A

If there is non disjunction in chromosome 21 in an ovum or sperm, one of the gametes will contain two copies of the chromosome. After fertilisation with a normal game the resulting zygote and embryo will have 3 copies of chromosome 21 causing varied physical and Menai development issues

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22
Q

What’s turners syndrome?

A

When there is non disjunction of the male sex chromosomes an egg may be fertilised by a sperm which has no sex chromosomes. The resulting genotype of the embryo will be XO. The affected person is apparently female however will not develop secondary sex characteristics and will be infertile. The development can be light to very severely stunted.

23
Q

What’s kleinfelter’s syndrome?

A

Non disjunction of the male sex chronometer can also result in a sperm with the sex chromosomes XY resulting in a zygote with the sex chromosomes XXY. The subject is apparently male but doesn’t develop secondary sex characteristics and will begin developing some breast tissue and have less muscle definition than normal. They may be indistinguishable or severely affected.

24
Q

Describe spermatogenesis pls

A

The diploid primordial germ cell divides several times by mitosis to form diploid spermatogonia.
The spermatogonia each grow without division until they can be called primary spermatocytes
Each primary spermatocyte divides via meiosis which results in two haploid secondary spermatocytes
The second meiotic division results in four haploid cells called spermatocytes
The spermatids then form into spermatozoa

25
Q

What is the acrosome?

A

The membrane bound storage site for enzymes that digest the layers surrounding the ovum and allow the sperms head to penetrate.

26
Q

What are the benefits to having condensed chromosomes in the sperms head?

A

The more condensed, the lighter, the less energy needed for it to be transported

27
Q

What are the microtubules role in the structure of a sperm cell?

A

The microtubules within the sperms flagella contract and relax creating a whip like movement which propels the sperm through its fluid environment.

28
Q

Mitochondria within sperm?

A

The mitochondria of sperm is tightly packed into the middle section. It provides the ATP for the whipping of the tail.

29
Q

What is gametogenesis?

A

Is the formation of the gametes by meiosis in the sex organs

30
Q

What does totipotent mean?

A

Means a cell is able to develop into all different cell types

31
Q

What is cleavage?

A

Is a process involving a special type of mitosis with no interphase that results in a mass of small, undifferentiated cells

32
Q

What is a blastocyst?

A

Is hollow ball of cells formed 5 days after fertilisation

33
Q

What are embryonic stem cells?

A

Are cells in the early embryo that have the potential to form many other types of cells

34
Q

What does pluripotent mean?

A

Means a cell is able to develop into most cell types but not all

35
Q

What are pluripotent embryonic stem cells?

A

Are embryonic stem cells that can form most but not all cells in the body

36
Q

What is cell determination?

A

Is the predestination of cells to become particular types of tissues from early in the development of the embryo

37
Q

What does it mean to differentiate?

A

It means to develop into specific types of tissues

38
Q

What are anthers?

A

Are the male sex organs in plants

39
Q

What is pollen?

A

It is produced in the anthers and contains the male haploid gamete in plants

40
Q

What are ovules?

A

Formed in the ovaries they contain the haploid female gamete in plants

41
Q

Describe oogenesis pls

A

Starts with one primordial germ cell which divides several times by mitosis to develop into oogonia
Only one oogonia moves on from here and Latrice amounts of material are added to this shell increasing its size dramatically.
Once per cycle in ovary a secondary oocyte forms which is the result of the primary oocyte dividing by miosis into a secondary and a polar body which dies.
The secondary oocyte is released during ovulation, if the cell is fertilised then it develops into a ovum and another polar body is released. The first polar body also divides

42
Q

What is a microspore?

A

Is formed by mitosis and is what all POLLEN cells are formed by

43
Q

What is a megaspore?

A

It is formed by mitosis and is what all EMBRYO SACS develop from

44
Q

What are the primordial germ cells?

A

Are the cells that divide by meiosis to ultimately form the sperm and ova

45
Q

Describe the process by which pollen grains are formed?

A
  • the pollen mother cell (microspore mother cell divides by meiosis twice to form four haploid cells.
  • each NUCLEUS divides once by MITOSIS to form one pollen tube nucleus and one generative nucleus.
  • when the pollen grain lands on the stigma of the plant two male gametes are produced by mitosis of the generative nucleus each gamete is just a haploid nucleus.
46
Q

Describe the process by which mature embryo sacs are formed

A

-The megaspore mothercell divides by meiosis to from four haploid cells three degenerate and one grow on.
-the cell grows on to be a megaspore or young embryo sac
- in total it divides 3 times by mitosis
-the final product is the mature embryo sac which contains:
Three antipodal cells
Two polar nuclei
One female gamete
Two synergies

47
Q

Describe the process of fertilisation in a plant

A
  • Firstly the pollen grain lands on the stigma of the style.
    The pollen tube nucleus produces enzymes which breaks down the plant tissue to burrow down the stigma towards the embryo sac.
  • the pollen tube nucleus burrows to the sac, the generative nucleus will divide during this time to form two haploid gametes.
  • the two male gametes are passed into the sac and double fertilisation occurs as one gamete fuses with the female gamete the other fuses with the two polar nuclei to form the endosperm nucleus
48
Q

Describe the structure of a pollen grain

A

They are comprised of:

  • A pollen tube nucleus
  • Cytoplasm
  • Thick Resistance Wall
  • Cell surface membrane
  • Generative nucleus (two male gametes)
49
Q

Describe the structure of a mature embryo sac

A

Two polar nuclei
One female gamete
Two synergies
Three antipodal cells

50
Q

Describe external fertilisation

A

Is the process of fertilisation in which the female and male gametes are released outside of the parental bodies to meet and fuse in the environment

51
Q

Describe internal fertilisation

A

Is the fertilisation of the female gamete by the male gamete which takes place inside the body of the mother

52
Q

Define germination

A

Is the process by which a pollen tube starts to grow out of the pollen grain to transfer the male nuclei to the nucleus

53
Q

What is double fertilisation?

A

It is the process which occurs in plants where one male gamete fuses with the female gamete to form the embryo, the other male gamete fuses with the two polar nuclei to form the endosperm nucleus

Biology A-LEVEL (12 decks)

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