3.4.6 and 3.4.3 Flashcards Preview

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Flashcards in 3.4.6 and 3.4.3 Deck (37)
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What is biodiversity?

the variety of living organisms in an area


What is a habitat?

place where an organism lives


What is a community?

all the populations of different species in a habitat


What levels can biodiversity be considered at?

local biodiversity - variety of species in a small habitat that's local to you
global biodiversity - variety of species on Earth (biodiversity is greatest at the equator and decreases towards the poles)


What is species richness?
-how is it worked out?

measure of the number of different species in a community
-by taking random samples of a community and counting the number of different species


What is species diversity?

the number of species in a community and the abundance of each species


How can biodiversity be measured?

calculate an index of diversity (d)

d = N (N-1)
sum of n (n-1)

N = total number of organisms of all species
n = total number of organisms of one species


The higher the value for index of diversity?

higher the number, the more diverse the area is


What is the index when all individuals are of the same species?



How do agricultural practices reduce biodiversity?

Woodland clearance - to increase area of farmland, directly reduces number of trees and number of species of trees, destroys habitats, species lose shelter and food source, so die or migrate, reducing biodiversity

Hedgerow removal - increases area of farmland by turning lots of small fields into fewer large fields, reduces biodiversity (same reasons as woodland clearance)

Pesticides - kill organisms (pests) that feed on crops, reduces biodiversity directly by killing pests, species that feed on pests lose a food source, so their numbers could decrease

Herbicides - kill weeds, reduces plant diversity and could reduce number of organisms that feed on weeds

Monoculture - fields containing only one type of plant, reduces biodiversity directly and supports fewer organisms (as habitat or food source), further decreases biodiversity


Examples of conservation schemes?

- legal protection of endangered species
-protected areas, SSSIs (sites of special scientific interest) and AONBs (areas of outstanding natural beauty) which restrict further development, including agricultural development
-Environmental Stewardship Scheme which encourages farmers to conserve biodiversity e.g. replanting hedgerows, leaving margins around fields for wild flowers to grow


What are gametes?

sex cells (sperm and egg)


What forms when sperm and egg join together?

zygote (which divides and develops into a new organism)


How are gametes different from human cells?

human cells have a diploid number of chromosomes (two of each chromosome) but gametes have a haploid number of chromosomes (one copy of each chromosome)


Why is fertilisation random?

any sperm can fertilise any egg


How does random fertilisation increase genetic diversity within a species?

random fertilisation produces zygotes with different combinations of chromosomes to both parents, this mixing of genetic material in sexual reproduction increases genetic diversity within a species


Where does meiosis take place?

reproductive organs


What happens to the chromosome number during meiosis?

the chromosome number halves
diploid cells ---> haploid cells


Describe the process of meiosis.

1. DNA unravels and replicates so there are two copies of each chromosome (chromatids)
2. DNA condenses to form double-armed chromosomes, each made from two sister chromatid joined in the middle by a centromere
3. Meiosis I - chromosomes arrange themselves into homologous pairs
4. homologous pairs are separated, halving the chromosome number
5. Meiosis II - sister chromatids are separated (centromere is divided)
6. four haploid cells (gametes) that are genetically different from each other are produced


What events during meiosis lead to genetic variation?

-crossing over
-independent segregation


What is crossing over in meiosis I?

-homologous pairs of chromosomes come together
-chromatids twist around each other and bits of chromatids swap over
-chromatids now contain different combinations of alleles
-so each of the four daughter cells will contain chromatids with different combinations of alleles


What is independent segregation in meiosis I?

-independent segregation means the pairs of homologous chromosomes can split up in any way
-so, daughter cells produced can contain any combination of maternal and paternal chromosomes with different alleles


What is produced by mitosis?

-cells with same number of chromosomes as parent cell
-daughter cells are genetically identical to each other and to the parent cell
-produces two daughter cells


What is produced by meiosis?

-cells with half the number of chromosomes as the parent cell
-daughter cells are genetically different from each other and the parent cell
-produces four daughter cells


What are the differences between mitosis and meiosis?

-mitosis involves one division (separates sister chromatids) but meiosis has two divisions (separates the homologous pairs then the sister chromatids)
-in mitosis, there's no pairing or separating of homologous chromosomes, and so no crossing over or independent segregation of chromosomes
-mitosis produces genetically identical daughter cells, unlike meiosis


When meiosis works properly, what is produced?

all four daughter cells end up with 23 whole chromosomes - one from each homologous pair


What happens when there are errors during meiosis ?

chromosome mutation - cells produced contain variations in the numbers of whole chromosomes or parts of chromosomes


What do chromosome mutations lead to?

inherited conditions because the errors are present in gametes (the hereditary cells)


What is non-disjunction?

chromosome mutation - failure of chromosomes to separate properly


How is Down's syndrome caused?

Down's syndrome is caused by having an extra copy of chromosome 21 (or sometimes an extra copy of part of chromosome 21)
non-disjunction means that chromosome 21 fails to separate properly during meiosis, so one cell gets an extra copy of 21 and the other gets none.
when the gamete with the extra copy fuses to another gamete at fertilisation, the resulting zygote will have three copies of chromosome 21