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DAT > SNS Biology - Reproduction > Flashcards

SNS Biology - Reproduction Flashcards

1
Q

Cell Division

Karyokinesis

A

Nuclear division

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2
Q

Cell Division

Cytokinesis

A

Cell division

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3
Q

Cell Division

Interphase

A
  • Cell normally spends at least 90% of its life in interphase
  • During this period, each chromosome is replicated
  • Invididual chromosomes are not visible - DNA is uncoiled - called chromatin
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4
Q

Cell Division

Prophase

A
  • Initiation of mitosis
  • Chromosomes condense
  • Centriole pairs separate and move towards opposite poles of the cell
  • Spindle apparatus forms between them and nuclear membrane dissolves allowing the spindle fibres to interact with the chromosomes
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5
Q

Cell Division

Metaphase

A
  • Centriole pairs are at opposite ends of the cell
  • Fibres of the spindle apparatus attach to each chromatid at the centromere to align the chromosmes at the centre of the cell forming the metaphase plate
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6
Q

Cell Division

Anaphase

A
  • Centromeres split so that each chromatid has its own distinct centromere, allowing sister chromatids to separate
  • Sister chromatids are pulled towards poles of the cell by shortening of the spindle fibres which are composed of microtubules
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7
Q

Cell Division

Telophase

A
  • Spindle apparatus dissolves
  • Nuclear membrane reforms
  • Each cell contains full complement of chromosomes
  • Chromosomes uncoil
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8
Q

Cell Division

Cytokinesis

A
  • Near the end of telophase, cytoplasm divides into two daughter cells each with a complete nucleus and its own set of organelles
  • In animals, cleavage furrow forms and cell membrane indents along equator of cell
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9
Q

Cell Division

Animal vs Plant Cells

A
  1. Plant cells lack centrioles. Spindle apparatus is synthesised by microtubule organising centres which aren’t visible
  2. While cytokinesis in animal cells proceeds through production of a cleavage furrow, plant cells are rigid and can’t form this. Instead, they divide by formation of a cell plate - expanding partition that grows outwards from the interior of the cell until reaches the cell membrane
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10
Q

Meiosis

Interphase

A
  • Parent cell’s chromosomes replicated
  • Generates 4N number of chromosomes
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11
Q

Meiosis

Prophase I

A
  1. Chromatin condenses into chromosomes
  2. Spindle apparatus forms, nucleoli and nuclear membranes disappear
  3. Synapsis and crossing over occur
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12
Q

Synapsis

A

Process by which homolous chromosomes come together and intertwine

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13
Q

Tetrad

A

During interphase I of meiosis, each chromosome consists of two sister chromatids, each synaptic pair of homologous chromosomes containds four chromatids and may be called a tetrad

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14
Q

Disjunction

A

Process by which homologous pairs of chromosomes separate and are pulled to opposite poles of the cell during anaphase I of meiosis

During disjunction, each chromosome of paternal origin separates (disjoins) from its homologue of maternal origin and either chromosome can end up in either daughter cell

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15
Q

Meiosis

Metaphase I

A
  1. Homologous pairs (tetrads) align at the equatorial plate
  2. Each pair attaches to a separate spindle fibre by its kinetochore
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16
Q

Meiosis

Anaphase I

A
  1. Disjunction occurs - thus distribution of homologous chromosomes to the two intermediate daughter cells is random with respect to parental origin.
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17
Q

Meiosis

Telophase I

A
  1. Nuclear membranes reform around each new nucleus
  2. Each chromosome still contains sister chromatids joined at the centromere
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18
Q

Meiosis II

A
  • Very similar to Meiosis I except is not preceded by chromosomal replication
  • Daughter cells contain haploid number of chromosomes
  • In human females, only one daughter cell becomes a functional gamete
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19
Q

Sexual Reproduction

Requirements

A
  1. Production of functional gametes by adult organisms
  2. Fertilisation or conjugation of these gametes
  3. Development of the zygote into another adult
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20
Q

Spermatogenesis

A
  • Occurs in seminiferous tubules of testes
  • Diploid cells - spermatogonia - undergo meiosis to produce four haploid sperm of equal size
  • Head consists almost entirely of the nucleus, flagellum propels the sperm cell
  • Mitochondria in the neck and body provide energy for locomotion
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21
Q

Oogenesis

A
  • Occurs in the ovaries
  • One diploid female sex cell undergoes meiosis to produce a single mature egg cell
  • Each meiotic division produces a polar body – a small cell that contains little more than the nucleus
  • The mature ovum is a large cell containing most of the cytoplasm, RNA, organelles and nutrients needed by developing embryos
  • Polar bodies rapidly degenerate
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22
Q

Spermatogenesis vs Oogenesis

A
  1. Polar bodies are produced in oogenesis only
  2. Oogenesis is discontinuous – a female is born with a given number of eggs arrested in prophase I. The first meiotic division is not completed until ovulation and the second, until fertilisation
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23
Q

Fertilisation
External

A
  • Occurs in vertebrates that reproduce in water (amphibians, fish)
  • The female lays eggs in the water and the male deposits sperm in the vicinity
  • Chances of fertilisation reduced considerably and many eggs laid to compensate
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24
Q

Fertilisation
Internal

A
  • Practised by terrestrial vertebrates
  • Provides direct route for sperm to reach the egg cell
  • Females produce fewer eggs
25
Q

Passage of Sperm

A

SEVEN UP
1. Seminiferous tubules
2. Epididymis
3. Vas Deferens
4. Ejaculatory duct
NOTHING
5. Urethra
6. Penis

26
Q

Site of Testosterone Production

A

Testes

27
Q

Follicle

A
  • Multilayered sac of cells which contains, nourishes and protects an immature ovum
  • Ovaries contain thousands of follicles
28
Q

Site of Oestrogen Production

A

Follicles of ovaries and corpus luteum

29
Q

Oestrogens

A
  • Steroid hormones
  • Stimulate the development of the female reproductive tract and contribute to the development of secondary sex characteristics
  • Also responsible for the thickening of the endometrium
30
Q

Progesterone

A
  • Steroid hormone
  • Secreted by the corpus luteum during the luteal phase of the menstrual cycle
  • Stimulates the development and maintenance of the endometrial walls in preparation for the implantation of athe zygote
31
Q

The Menstrual Cycle
Follicular Phase

A
  1. Reproductive hormone levels are at their lowest, shutting off negative feedback signalling to the hypothalamus
  2. Hypothalamus releases GnRH
  3. Stimulates release of FSH from the anterior pituitary
  4. FSH promotes the development of the follicle within the ovary
  5. Ovary grow and begins to secrete oestrogen
32
Q

The Menstrual Cycle
Ovulation

A
  1. Midway through the cycle, is a surge in LH levels, preceded and caused by a peak in oestrogen levels created by the mature follicle
  2. A mature follicle bursts and releases an ovum
  3. Ovum is captured by the oviduct
33
Q

The Menstrual Cycle
Luteal Phase

A
  1. Following ovulation, LH induces the ruptured follicle to develop into the corpus luteum
  2. This secretes oestrogen and progesterone
  3. Progesterone causes the glands of the endometrium to mature and produce secretions that prepare the uterus for the implantation of an embryo
34
Q

The Menstrual Cycle
Menstuation

A
  1. If the ovum isn’t fertilised, the corpus luteum atrophies
  2. Resulting drop in oestrogen and progesterone levels causes the endometrium to slough off
35
Q

The Menstrual Cycle
Fertilisation

A
  1. If fertilisation occurs, the developing placenta produces hCG which maintains the corpus luteum and thus the supply of oestrogen and progesterone until the placenta takes over production
36
Q

Sexual Reproduction in Plants

A
  • Alternates between the dipoid sporophyte generation and the hapoid gametophyte generation
  • Relative lengths of the two stages vary with plant type
  • Thus gametophytes reproduce sexually, sporophyte generation reproduces asexually
37
Q

Sexual Reproduction in Plants
Gametophyte Generation

A
  • Haploid gametophyte generation
  • Produces gametes by mitosis
  • Union of the male and female gametes at fertilisation restores diploid sporophyte generation
  • Dominant form in mosses
38
Q

Sexual Reproduction in Plants
Sporophyte Generation

A
  • Diploid gametophyte generation
  • Produces a haploid (monoploid) spore by meiosis
  • Spores divide by meiosis to produce the haploid gametophyte generation
  • Dominant form in ferns
39
Q

Sexual Reproduction in Plants
Angiosperms

A
  • Flowering plants
  • Have gametophytes consisting of a few cells that exist for a very short time
  • Some plants have only stamens (male plants) and some only pistils (female plants)
40
Q

Sexual Reproduction in Plants
Angiosperms
Parts

A
  1. Stamen
  2. Pistil
  3. Petals
  4. Sepals
41
Q

Sexual Reproduction in Plants
Angiosperms
Parts
Stamen

A
  • Male organ of flower
  • Consists of thin stalk-like filament with a terminal sac called an anther
  • Anther produces haploid spores that develop into pollen grains
42
Q

Sexual Reproduction in Plants
Angiosperms
Parts
Pistil

A

• Female organ of the flower
• Consists of three parts:
1. Stigma – sticky part at top of pistil that catches pollen
2. Style – tube-like structure connecting the stigma to the ovary
3. Ovary – enlarged base of pistil. Contains one or more ovules. Each ovule contains a monoploid egg nucleus

43
Q

Sexual Reproduction in Plants
Angiosperms
Parts
Petal

A
  • Specialised leaf surrounding and protecting the pistil
  • Characteristic colours and scents attract insects which transfer pollen between plants and enable fertilisation
44
Q

Sexual Reproduction in Plants
Angiosperms
Parts
Sepal

A

• Green leaves covering and protecting the flower bud during early development

45
Q

Sexual Reproduction in Plants
Angiosperms
Fertilisation
Male Gametophyte

A
  • Pollen grain
  • Contains the tube nucleus and a generative nucleus formed by mitosis of the microspore
  • Transferred from the anther to the stigma and the generative nucleus divides to form sperm nuclei which are the male gametes
46
Q

Sexual Reproduction in Plants
Angiosperms
Fertilisation
Female Gametophyte

A
  • Embryo sac containing nuclei including the two polar nuclei (endosperms) and the egg nucleus
  • Develops in the ovule from one of four spores
47
Q

Sexual Reproduction in Plants
Angiosperms
Fertilisation

A
  • Occurs when the sperm nuclei enter the embryo sac
  • One sperm nucleus fuses with the egg nucleus to form the diploid zygote which develops into the embryo
  • The other sperm nucleus fuses with the two polar bodies to form the endosperm (triploid, 3N) which provides food for the embryonic plant
48
Q

Asexual Reproduction
Mechanisms

A
  1. Binary Fission
  2. Budding
  3. Regeneration
  4. Parthogenesis
49
Q

Asexual Reproduction
Mechanisms
Binary Fission

A

• DNA replicates and a new plasma membrane and cell wall grow inwards along the cell midline dividing it into two new, equally sized cells

50
Q

Asexual Reproduction
Mechanisms
Binary Fission
Organisms

A

• Seen in one-celled prokaryotic organisms

  1. amoebae
  2. algae,
  3. bacteria
  4. paramecia
51
Q

Asexual Reproduction
Mechanisms
Budding

A
  • Replication of the nucleus followed by unequal cytokinesis
  • Cell membrane pinches inward to form a new cell which is smaller but genetically identical to the parent cell and subsequently grows to adult size
  • May detach immediately or remain attached
52
Q

Asexual Reproduction
Mechanisms
Budding
Organisms

A
  1. Hydra
  2. Yeast
53
Q

Asexual Reproduction
Mechanisms
Regeneration

A
  • Regrowth of a lost or injured body part
  • Replacement of cells occurs by mitosis
  • Some animals such as starfish have extensive regenerative capacities. Severed arm may even be able to regenerate an entire body as long as contains a piece of an area called the central disk
54
Q

Asexual Reproduction
Mechanisms
Parthenogenesis

A
  • Development of an unfertilised egg into an adult organism
  • Occurs naturally in certain lower organisms
  • For example, in most species ants and bees, males develop from unfertilised eggs whilst the worker and queen bees develop from fertilised eggs
  • Artificial parthenogenesis can be performed in some animals, for example rabbits and frogs
55
Q

Asexual Reproduction In Plants
Mechanisms

A
  1. Spore formation
  2. Natural vegetative propagation
  3. Artificial vegetative propagation
56
Q

Asexual Reproduction In Plants
Mechanisms
Spore Formation

A
  • All plants exhibit alternation of generations in which diploid generation is succeeded by haploid generation
  • The sporophyte generation produces haploid spores that develop into the gametophyte generation
57
Q

Asexual Reproduction In Plants
Mechanisms
Natural Vegetative Propagation

A

• Meristems (undifferentiated tissues in plants) provide a source of cells that can develop into an adult plant

  1. Bulbs – split to form new bulbs (tulpis, daffodils)
  2. Rhizomes – woody, underground stems that can develop into new upright stems (ferns, iris plants)
  3. Runners – stems running above and along the ground extending from the main stem that can produce new roots and upright stems (strawberry plants, lawn grasses)
  4. Tubers – underground stems with buds that can develop into adult plants
58
Q

Asexual Reproduction In Plants
Mechanisms
Artificial Vegetative Propagation

A
  • Cut piece of stem can develop new roots in water. Auxins can be used to accelerate root formation
  • Stems of certain plants (eg blackberry, raspberry) will take root when bent to the ground and covered with soil – latering

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