test 2:

Question 1

Chromosome:

Answer 1

threadlike structure containing DNA visible during mitosis

Question 2

Chromatin:

Answer 2

combinations of DNA wound around histones proteins (basic)

Question 3

Chromatid:

Answer 3

a single arm of the X-shaped chromosome

Question 4

organization of Eukaryotic chromosomes:

Answer 4

1) DNA double helix
2) DNA wrapped around histones
3) Nucleosomes coiled into a chromatin fibre
4) Further condensation of chromatin
5) Duplicated chromosome

Question 5

Stages of the cell cycle:

Answer 5

1. Interphase (cell growth)
   -G1 phase
   -S phase (DNA synthesis)
   -G2 phase
2. Mitosis
3. Cytokinesis

Question 6

Interphase:

Answer 6

cell grows to its normal size after cell division, and synthesises important substances, e.g. proteins

Question 7

Growth 1 phase:

Answer 7

-gap after cell division and before S phase
-46 chromosomes and chromatid at this phase
-prepares for growth and DNA synthesis (S phase) by producing RNA, proteins and enzymes
-new organelles are formed
-if there are insufficient growth factors, or when cell has reached its maximum size, cell will not divide and remain in G1

Question 8

S phase:

Answer 8

-synthesis of DNA, each chromosome consists of two identical chromatids
-46 chromosomes and 92 chromatid at this stage
-chromatin also replicates along with DNA so histones are replicated

Question 9

Growth 2 phase:

Answer 9

-gap after S phase and before nuclear division (prepares for mitosis)
-new DNA checked, and errors are repaired
-centrioles replicate
-food storage is increased

Question 10

Mitosis:

Answer 10

nuclear division producing two genetically identical daughter nuclei, each containing the same number of chromosomes as the parent

Question 11

Stages of Mitosis:

Answer 11

1) Prophase
2) Metaphase
3) Anaphase
4) Telphase
5*) Cytokinesis

Question 12

Prophase:

Answer 12

-chromosomes condense and become visible
-spindle fibres emerge from the centrosomes
-nuclear envelope breaks down
Note: nuclear envelope breaks down into vesicles during prophase and reassembles when the vesicles fuse to form the envelope back at telophase
-nucleolus disappears

Question 13

Metaphase:

Answer 13

-mitotic spindle is fully developed, centrosomes are at opposite poles of the cell
-chromosomes are lined up at the metaphase plate
-each sister chromatid is attached to a spindle fiber originating from opposite poles

Question 14

Anaphase:

Answer 14

-cohesion preotins binding the sister chromatids together break down
-sister chromatids (now called chromosomes) are pulled toward opposite poles
-non-kinetochore spindle fibres lengthen, elongating the cell

Question 15

Telophase:

Answer 15

-chromosomes arrive at opposite poles and begin to decondense
-nuclear envelope material surrounds each set of chromosomes
-the mitotic spindle breaks down

Question 16

Cytokinesis:

Answer 16

division of cytoplasm between daughter cells, last stage of cell division, it results in the formation of 2 cells

Question 17

Significance of mitosis:

Answer 17

-growth: clones produced allow growth of multicellular organism from unicellular zygote
-replacement of cells and repair of tissues: cells die and are replaced; rapid in skin, lining of gut, and to regenerate whole parts of body

Question 18

Asexual reproduction:

Answer 18

-> production of a new individual by a single parent
-in unicellular organisms, cell division results in reproduction
-in multicellular organisms, new individuals produced bud off from parent

Question 19

Mitotic index:

Answer 19

a measure of how actively cells are dividing in a given tissue
Mitotic index = cells in mitosis/total number of cells x 100

Question 20

Sexual reproduction: features

Answer 20

-formation of gametes
-uses meiosis cell division
-leads to genetic variation

Question 21

Sexual reproduction: disadvantages

Answer 21

-hard to find mates
-resources wasted by forming gametes

Question 22

Meiosis:

Answer 22

Chromosomes are halved from diploid (2n) cells to haploid (n) cells
-thus, chromosome number is kept constant instead of doubling every generation

Question 23

Meiosis: stages

Answer 23

1) Prophase I
2) Metaphase I
3) Anapphase I
4) Telophase I and cytokinesis
5) Prophase II
6) Metaphase II
7) Anaphase II
Telophase II and cytokinesis

Question 24

Prophase I:

Answer 24

the chromosomes condense, and the nuclear envelope breaks down, crossing over occurs

Question 25

Metaphase I:

Answer 25

pairs of homologous chromosomes move to the equator of the cell

Question 26

Anaphase I:

Answer 26

homologous chromosomes move to the opposite poles of the cell

Question 27

Telophase I and cytokinesis:

Answer 27

chromosomes gather at the poles of the cells -the cytoplasm divides

Question 28

Prophase II:

Answer 28

a new spindle forms around the chromosomes

Question 29

Metaphase II:

Answer 29

metaphase II chromosomes line up at the equator

Question 30

Anaphase II:

Answer 30

centromeres divide, chromatids move to the opposite poles of the cells

Question 31

Telophase II and cytokinesis:

Answer 31

a nuclear envelope forms around each set of chromosomes, the cytoplasm divides

Question 32

Independent assortment:

Answer 32

-occurs during Metaphase I -pairs of homologous chromosomes lie independently of each other and randomly at the equator, therefore genetically different gametes fuse at random

Question 33

Crossing over:

Answer 33

-> occurs during prophase I, homologous chromosomes pair up along the length of all four chromatids -chiasmata is formed between bivalent chromosomes, it connects with a non-sister chromatid so maternal and paternal genes are exchanged -several of these occur resulting in large amounts of variation -some genes are linked which affects how it is inherited in an offspring during crossing-over -genes located close to each other are strongly linked as they are unlikely to separated during crossing-over, so they are more likely to be inherited together -genes located far from each other are loosely linked as they are likely to separate during crossing-over, so they are less likely to be inherited together

Question 34

Sperm cell structure: acrosome

Answer 34

a membrane-bound storage site for enzymes that digest the layers surrounding the ovum to penetrate it

Question 35

Sperm cell structure: haploid nucleus:

Answer 35

contains highly condensed genetic material, containing half the number of chromosomes of the organism -therefore less energy is required to carry it

Question 36

Sperm cell structure: Neck

Answer 36

tightly packed mitochondrion is present, they provide energy or lashing the tail to move

Question 37

Sperm cell structure: tail

Answer 37

a complex flagellum that creates a whipping motion to propel it forwards

Question 38

Egg cell structure: zona pellucida

Answer 38

a jelly-like layer surrounding the oocyte; controls sperm entrance

Question 39

Egg cell structure: cytoplasm

Answer 39

stores large amounts of food

Question 40

Egg cell structure: follicle cells

Answer 40

surrounds the zona pellucida, they are left over from the ovulation process

Question 41

Egg cell structure: cortical granules + lipid droplets

Answer 41

specializes lysosomes that activate when sperm enters the cell, causing the zona pellucida to harden -this prevent polyspermy fertilization

Question 42

Egg cell structure: haploid nucleus

Answer 42

Genetic material, containing half the number of chromosomes of the organism

Question 43

Male gamete in plants (pollen grain):

Answer 43

-tube nucleus: controls the growth of the pollen tube as well as release of hydrolytic (digestive) enzymes -generative nucleus: divided by mitosis into two sperm nuclei for fertilisation

Question 44

Female gamete (embryo sac):

Answer 44

-egg cell: contains half the number of chromosomes of the organism and fuses with one of the sperm nuclei, forming a diploid zygote -polar nuclei: contains half the number of chromosomes of the organism and fuses with one of the sperm nuclei, forming a triploid endosperm

Question 45

Fertilisation: mammals

Answer 45

-cells are surrounding the secondary oocyte release chemicals, attracting the sperm cells -once sperm reaches the secondary oocyte, an acrosome reaction occurs -enzymes are released, they begin digesting the follicle and zona pellucida layers -the enzymes are released by exocytosis from the sperm head -once digested, the sperm nucleus de condenses, then, it’s released by exocytosis into the secondary oocyte release chemicals -the cortical reaction takes place, releasing enzymes that cause hardening of the zona pellucida, this prevents other sperm cells from entering -the genetical material is taken into the cell by endocytosis, this triggers Meiosis II to form an ovum -the haploid nuclei fuse, forming a diploid zygote

Question 46

Fertilisation:

Answer 46

-once a pollen reaches the stigma surface, it starts germinating after absorbing the sugar solution on its surfaces -the pollen tube starts growing towards the embryo via chemical stimulus -the tube nucleus releases enzymes by exocytosis, allowing the formation of a tube -as the tube elongates, nutrients are absorbed along the way -the generative nucleus divides producing 2 sperm nuclei -the pollen tube reaches the micropyle (the entrance to the embryo), penetrating the embryo sac wall -double fertilisation occurs, which 1 nucleus fuses with the egg cell, forming a diploid zygote- the other nucleus fuses with the 2 polar nuclei, forming a triploid endosperm nucleus -after fertilisation, the ovule becomes a seed, the zygote becomes an embryo, and the endosperm becomes food storage