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biology > ch 18 > Flashcards

ch 18 Flashcards

1
Q

what is a chromosome made up of

A

-2 chromatids joined together
-chromatids are coiled threads of DNA

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2
Q

define gene

A

a dna segment

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3
Q

what do genes determine

A

the genetic characters

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4
Q

how does DNA control cell functions [3]

A

-cell functions are controlled by proteins
-these proteins consist of a sequence of amino acids
-this sequence of amino acids is determined by the sequence of nitrogen bases

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5
Q

what is a homologous series of chromosomes [2]

A

a pair of chromosomes that are similair in length , same number of genes , same order of genes
-one chromosome is maternal and one is paternal

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6
Q

what are alleles [3]

A

-a pair of genes
-controlling the same genetic characters
-and occupying the same position on homologous chromosomes

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7
Q

what is an allele

A

alternative form of a gene

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8
Q

how does mitosis occurs [4]

A

-when parent cell gives 2 daughter cells
-parent cell is diploid and daughter cells are diploid
-no. of chromosomes are doubled
-by asexual reproduction

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9
Q

where does mitosis occur and why?

A

occurs in most body cells
-for growth and tissue repair

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10
Q

advantage of mitosis and explnation for that

A

-maintains genetic stability , because daughter cells are identical to the parent cells , no evolution

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11
Q

how does meiosis occur [4]

A
  • 1 parent cell gives 4 daughter cells
    -parent cell is diploid but daughter cells are haploid
    -no. of chromoses is halved
    -sexual reproduction
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12
Q

where does meiosis occura

A

in sex cells for production of gametes

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13
Q

what are stem cells

A

non specialized cells that divide by mitosis to produce daughter cells that can become specialized to do specifc functions

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14
Q

give 2 examples of stem cells and what they do

A

-in embryo, become specialized to form skin, hair, muscles and bone cells
-in bone marrow, become specialized to form different blood cells

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15
Q

define autosomes , and state how many in a cell

A

they are chromosomes which determine all genetic characters except sex
-44 chromoses in cell

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16
Q

define sex chromosomes , and state how many in a cell

A

-they are sex chromosomes which determine sex
represented by X (longer) and Y (shorter)
_male =XY and female =XX
-2 per cell

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17
Q

define diploid cell

A

a cell which contain full number of chromosomes

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18
Q

define haploid cell

A

a cell which contain half the number of chromosomes

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19
Q

define phenotype

A

it is the observable characters of the organism which are genetically determined

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20
Q

define genotype

A

it is the genetic make up of the organism or the alleles present inside the cells of the organism

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21
Q

define dominant gene [2]

A

-a gene which can show its effect in the phenotype of the organsim
-it masks the recessive gene

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22
Q

define recessive gene [2]

A

-a gene which cant show its effect in the phenotype of the organism
-it is masked by the dominant gene

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23
Q

define homozygous organism

A

an organsim which contains in its genotype 2 identical alleles for the same character

24
Q

define heterozygous organisn

A

an organism which contains in its genotype 2 different alleles for the same character

25
describe sex inheritance in humans [5]z
-during meiosis in the ovary each ovum receieves one of the X chromosomes , so all of the ova have X chromosome -in the testis % of the sperms get X chromosome and 50% get Y chromosome -if an X sperm fertilizes an ovum , the zygote will be XX and will develop into a girl -if Y sperm fertilizes an ovum , the zygote will be XY and will develop into a bpy -there is an equal chance of an X or Y fertilizing an ovum
26
what are sex-linked genes
X chromosome is longer than Y chromosome , so some genes are present on X chromosome, only
27
why are sex--linked diseases more common in males than females
because no male carrier, so sex linked diseases is more common in males
28
how can 2 normal parents produce an affected child?
both parents are heterozygous normal , so child will recieve one recessive allele from each parent to become homozygous recessive
29
define variation
it is the observale difference within a species
30
types of variation [2]
-continous -discontinous
31
compare continous and discontinous variation [6]
-in discontinous from the moment of birth till death the the sex or blood group are constant (dont change by time) but in continous from the moment of birth till death the height or intelligence are changing with time -in discontinous there are clear phenotypes (male or female) but in continous there are no clear phenotypes -in discontinous no intermmediate forms but in continous many intermediate forms (ex: height: v tall, tall, avg, short, v. short) -in discontinous controlled by 1 pair of alleles but in continous controlled by several types of alleles -in dis. not affected by enviroment and continous is affected by enviroment -in dis its represented by bar chart but in continous its represneted by curve
32
causes of genetic variation [3]
-meiosis: produces haploid gametes -fertilization : random fusion of gametes -mutation: cause change in the genes , by change in sequence of nitrogen bases
33
how variation can lead to evolution through natural selection? [5]
-genetic variation -a change in external enviroment -struggle for existence, both varities are going to struggle with each other -survival of the fittest, one variety could adapt itself to the changes in the surronding enviroment so it survives and lives longer (so one variety evolves and the other cant so it goes extinct) -natural selection, by this way the nature has selected one variety to live which has a selective advantage while the other one doesnt which have selective disadvantage
34
precautions while using antibiotics [3]
-dont use antibiotics unless they are strictly indicated by doctors -dont use only one type of antibiotics , but use different types -dont take incomplete course of antibiotics
35
why do we take precaution with antibiotics
to avoid resistance of bacteria to antibiotics
36
explain why is it important to complete a full treatment of antibiotics []
-all bacteria need to be killed or any remaining bacteria will mutiply and disease will continue -antibiotic resistance, so antibiotic will no longer be effective
37
how mutation of bacteria can lead to evolution ?
mutation of bacteria produced mutant bacteria that are resistant to antibiotics so they surivied , live longer and made evolution
38
how survival of the fittest lead to evolution
when the more fit organism survives , they reproduce and pass on their alleles to the next generations
39
how natural selection can lead to adaptations [2]
- nature selects one variety ,to survive on the expense on the other variety -the selected variety is more suited to the surronding enviroment
40
define adaptation
a process resulting from natural selection, by which population become more suited to surronding enviroment
41
what is artificial selection [3]
-humans choose animals or plants with best desirable characteristics and allow them to breed together - to produce offspring with high economic importance -the process of selective breeding is repeated many times over many generations
42
compare natural selection and artificial selection [3]
-natural selection is caused by nature (enviromental pressure) but artificial selection is caused by humans -natural selection has more variation but artificial selection has less variation -natural selection is slower
43
define mutation
it is change in base sequence in DNA
44
causes of mutation [2]
-radations -chemicals
45
where mutations may occur [2]
-somatic cells -sex cells
46
what happens if mutation occur in somatic cells
cause cancer
47
how can mutation occur in sex cells [2]
-chromosome mutation -gene mutation
48
what are adaptive features
it is inherited feature that helps the organism to survive and live longer and reproduve in its enviroment
49
what are xerophytes
desert plants,that grow inhabitats very hot and dry
50
describe the roots of xerophytes [2]
-very long and branching , to absorb as much water as possible from the soil -has conc. cell sap to increase absorbtion of water by osmosis
51
describe the stem of xerophytes [3]
-short, to resist breaking by wind -swollen, to store water -green, to make photosynthesis instead of spiny leaves
52
describe the leaves of xerophytes [4]
-thick cuticle, to reduce water loss by transpiration -few stomata sunken in grooves, to reduce water loss by transpiration -rolled in edges (less surface area) , to reduce water loss by transpiration -hairs , to trap water vapour inside the grooves of the leaf
53
desert leaf may sometimes change to spines or leaves with very little surface area ..why is this a disadvantage of the plant?
less surface area so less absorbtion of light so less photosyntheis so less plant nutrition
54
what are hydrophytes
plants that live in aquatic habitats
55
describe roots of hydrophytes
either missing or small roots floating freely in water, because water plants dont need fixation or water absorbtion (they are surronded by water
56
describe stems of hydrophytes
no xylem and no lignin, to be flexible with water current and has much air spaces to float to surface to absorb light and CO2
57
describe leaves of hydrophytes [3]
-much air specaes -stomata on upper surface to absorb co2 -no stomata on lower surface , not to uptake water get heavy and sink

biology (19 decks)

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