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Edexcel A Level Biology > Topic 4 > Flashcards

Topic 4 Flashcards

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1
Q

What does a niche refer to?

A

How an organism fits into its ecosystem as a result of behavioural, physiological, and anatomical adaptations

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2
Q

What are behavioural adaptations?

A

Ways in which an organism acts that increase the chance of survival

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3
Q

What are physiological adaptations?

A

Processes inside an organism’s body that increase the chance of survival

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4
Q

What are anatomical adaptations?

A

Structural features that increase the chance of survival

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5
Q

How do useful adaptations become more common within a population?

A

Selection pressures create a struggle for survival. Individuals without the useful alleles don’t survive to pass on their genes. Individuals with the useful alleles do survive and have offspring, making these alleles more common.

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6
Q

How does reproductive isolation lead to speciation?

A
  • Seasonal changes- different flowering/mating seasons
  • Mechanical changes- changes to genitalia, preventing successful mating
  • Behavioural changes- rituals that aren’t attractive to main population
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7
Q

What is the Hardy-Weinburg equation?

A

p^2 + 2pq + q^2 =1

Where p^2= frequency of homozygous dominant, 2pq= frequency of heterozygous, q^2= homozygous recessive

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8
Q

What are the assumptions needed to use the Hardy-Weinburg equation?

A
  • large population
  • no immigration or emigration
  • no natural selection/mutations
  • random breeding
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9
Q

How is biodiversity defined?

A

The number and abundance of different species, as well as genetic diversity within a species

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10
Q

What is endemism?

A

When a species is unique to one location

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11
Q

How is genetic diversity measured?

A

Using a heterozygosity index, with a higher proportion of heterozygotes meaning higher genetic diversity.
H= number of heterozygotes/population

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12
Q

How is species diversity measured?

A

D=(N(N-1)/∑(n)(n-1)

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

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13
Q

What does a high D value show?

A

The area is very biodiverse

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14
Q

How are species classified?

A

By genotypes and by phenotypes

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15
Q

What are the classifications, going from least to most related?

A 
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
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16
Q

How has classification changed over the last 200 years?

A

Early classification depended solely on species’ phenotypes and scientists disagreed on the relative importance of features. New technology means that genotypes can be analysed to determine how closely species are related.

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17
Q

What is molecular phylogeny?

A

The use of a gene’s molecular characteristics to classify an organism and to place it on a map of evolutionary relationships.

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18
Q

Name eight organelles plant cells have that animal cells don’t

A

Cell wall, chloroplasts, amyloplasts, vacuole, tonoplast, plasmodesmata, pits, middle lamella

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19
Q

Function of cell wall?

A

Supports plant cells, giving them a rigid structure

20
Q

Function of chloroplasts?

A

Where photosynthesis takes place

21
Q

Structure of chloroplasts?

A

Flattened structure and surrounded by double membrane

22
Q

Function of amyloplasts?

A

Storage of starch grains and the conversion of starch back to glucose when needed

23
Q

Function of vacuole?

A

To keep cell turgid, and to isolate and break down unwanted chemicals

24
Q

Function of tonoplast?

A

It controls what enters and leaves cell

25
Q

Function of plasmodesmata?

A

It allows the transport of substances and communication between cells

26
Q

Function of pits?

A

They allow transport of substances between cells

27
Q

Function of middle lamella?

A

It acts as an adhesive, sticking plant cells together. This gives plants stability.

28
Q

What is the cohesion-tension theory?

A

The water forms a continuous pathway from the mesophyll cells and down the xylem. The reason why water forms this continuous pathway is due to the cohesion between water molecules. Water is pulled up behind the evaporating water due to the cohesion.
Therefore: water is constantly being pulled up the xylem as a result of transpiration. This transpiration pull puts the xylem under tension.

29
Q

What is cohesion?

A

Hydrogen bonds between two water molecules

30
Q

What is adhesion?

A

Hydrogen bonds between water and cell wall

31
Q

Define the term transpiration

A

The passage of water through a plant from the roots through the vascular system to the atmosphere.

32
Q

Give the mechanism for transpiration

A

1) Water vapour diffuses out through the stroma
2) It then evaporates from surfaces of cells lining substomatal cavities
3) Water is replaced by means of capillary action within cell walls
4) Water is drawn out of the xylem, from a continuous column of water

33
Q

Give the main features of cellulose.

A
  • Long, unbranched chains of beta-glucose, joined by 1-4 glycosidic bonds
  • 50-80 cellulose chains, linked together by lots of H-bonds, form microfibrils
  • Microfibrils mean that cellulose can provide structural support for cells
34
Q

What are three types of fibres in plants?

A

Xylem, phloem, and sclerenchyma fibres

35
Q

What is the function of xylem fibres?

A

It transports water and mineral ions up the plant, and provides support

36
Q

How have xylem fibres adapted to their function?

A

They are found in long tube-like structures, formed from dead cells being joined end-to-end.
They have a hollow lumen and no end walls, which allow water and mineral ions to pass through easily
The walls are thickened with lignin to support the plant.
There are pits in the walls to let water and mineral ions in and out of the xylem

37
Q

What is the function of sclerenchyma fibres?

A

To provide structure for the plant

38
Q

How have sclerenchyma fibres adapted to their function?

A

Sclerenchyma fibres are made of bundles of dead fibres that run vertically up the plant. They have cell walls that are thickened with lignin. They also have more cellulose than other plant cells

39
Q

What is the function of phloem fibres?

A

To transport organic solutes from where they’re made to where they’re needed.

40
Q

How have phloem fibres adapted to their function?

A

Phloem tissues are made up of two types of cell: sieve tube elements, and companion cells

41
Q

What are sieve tube elements?

A

They are living cells that form a tube-like structure. The end walls have lots of pores to let solutes pass through. They don’t have a nucleus, have a thin layer of cytoplasm and have very few organelles.

42
Q

Why are companion cells needed?

A

Sieve tube elements can’t survive on their own because they don’t have a nucleus. Companion cells carry out living functions for both themselves and their sieve tube element.

43
Q

Explain why plant fibres are strong.

A
  • The cell walls contain cellulose microfibrils in a net-like arrangement, which gives fibres their strength
  • Some structural cells produce a secondary well when they finish growing. The secondary wall is thicker than normal and contains more lignin.
44
Q

What nutrients are essential to plants?

A

Water, magnesium ions, nitrate ions, calcium ions

45
Q

Explain why plants need water, and what would happen if water was deficient.

A

Water is needed for: photosynthesis, transportation of minerals, structural rigidity, and temperature regulation. If a plant didn’t have enough water, all of these would become inefficient.

46
Q

Explain why plants need magnesium ions, and what would happen if it was deficient.

A

Mg2+ is needed for chlorophyll production. A lack of magnesium ions will mean that the plant wouldn’t be able to photosynthesise properly

Edexcel A Level Biology (8 decks)

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