Bio Paper One Part 2 Flashcards
(113 cards)
1
Q
What risk does diet have associated with cardiovascular disease
A
High salt increases blood pressure
High levels of saturated fats raise blood cholesterol
Antioxidant rich food reduced risk
2
Q
What is transpiration
A
The evaporation of water from mesophyll cells followed by the diffusion of water vapor through stomata into the atmosphere
3
Q
Why does water move from air spaces in the leaf to the atmosphere?
A
The humidity of the atmosphere is usually lower than that inside the leaf, creating a water potential gradient. This causes water vapor to diffuse out through the stomata.
4
Q
How is water lost from air spaces replaced?
A
By evaporation of water from the mesophyll cell walls into the air spaces.
5
Q
How do plants control transpiration?
A
By changing size of their stomata pores
6
Q
How do mesophyll cells lose water during movement of water across cells of a leaf
A
Water evaporates from their cell walls into the air spaces of the leaf due to heat from the sun
7
Q
Q: What is the consequence of water loss from mesophyll cells?
A
It lowers their water potential, causing water to move in from neighboring cells via osmosis.
8
Q
How does water move through the mesophyll cells?
A
Water evaporates from mesophyll cells.
These cells now have a lower water potential.
Water moves into them from neighboring cells by osmosis.
This process continues, creating a water potential gradient across the leaf
9
Q
Why is a water potential gradient important?
A
It ensures a continuous flow of water from the xylem, through the leaf, and eventually into the atmosphere.
10
Q
What force primarily pulls water from the xylem?
A
The cohesion-tension mechanism, which relies on hydrogen bonding between water molecules
11
Q
How does transpiration drive water movement?
A
Water evaporates from mesophyll cells due to heat from the sun (transpiration).
Water molecules form hydrogen bonds and stick together (cohesion).
This creates a continuous, unbroken column of water moving up the xylem.
As water evaporates from leaf air spaces, more water is drawn up due to cohesion.
This results in negative pressure (tension) within the xylem, pulling water upwards.
12
Q
Define transpiration pull and its role in water transport
A
Transpiration pull is the tension created in the xylem due to water loss from the leaves.
This tension pulls water upwards through the plant in a continuous stream.
It is passive and requires no metabolic energy.
13
Q
How does tree trunk diameter change with transpiration rates?
A
During the day, transpiration is high, creating more tension in the xylem. This pulls the xylem walls inward, causing the trunk to shrink.
At night, transpiration is lower, reducing tension, so the trunk expands as the xylem walls relax. Provides evidence for cohesion theory
14
Q
What happens when a xylem vessel is broken?
A
Air is drawn in, instead of water leaking out, proving that xylem is under negative pressure(means lower than atmospheric pressure) (tension).
Water can no longer be pulled up because the continuous column of water is broken.
15
Q
Is energy required for water movement in the xylem? Why or why not
A
No, transpiration pull is passive.
Xylem vessels are dead, hollow tubes, meaning no metabolic energy is required for water movement.
The only energy required comes from the sun, which evaporates water from the leaves, driving transpiration.
16
Q
How do xylem vessel structure and properties support water movement?
A
Lignified walls prevent collapse under tension.
Continuous hollow tubes allow uninterrupted water movement.
Hydrogen bonding between water molecules causes cohesion, maintaining a continuous column of water.
No organelles
17
Q
How does cutting a plant stem affect water transport?
A
It breaks the continuous water column, stopping water movement because cohesion is lost.
18
Q
What effect would increasing humidity have on transpiration and water movement?
A
High humidity reduces transpiration by lowering the water potential gradient between leaf air spaces and the atmosphere.
This decreases the tension in the xylem, slowing down water movement.
19
Q
Why is it difficult to measure transpiration directly?
A
Because water vapor is hard to condense and collect for measurement
20
Q
What method is used to measure water uptake instead?
A
A potometer, which measures the rate of water uptake by a plant.
21
Q
Why is water uptake a good estimate for transpiration rate?
A
About 99% of the water taken up by a plant is lost through transpiration, so uptake closely matches transpiration rate under constant conditions.
22
Q
How do environmental factors affect water uptake?
A
More stomata open → Higher uptake.
Higher wind speed or lower humidity → Increased uptake due to a greater water potential gradient.
23
Q
What is the formula for calculating the rate of water uptake in a potometer experiment?
A
Rate of uptake = distance moved x pi r squared/time taken
Where pi r squared are cross section of tubes and r is radius of tube
24
Q
What is translocation?
A
The process by which organic molecules (e.g., sugars) and some minerals are transported from one part of a plant to another via the phloem.
25
What is the phloem made up of?
Sieve tube elements: Long, thin structures arranged end to end with sieve plates that have tiny holes to allow transport.
Companion cells: Support sieve tube elements by providing ATP and metabolic functions.
26
How does the structure of sieve tube elements help in translocation?
Sieve plates have pores that allow organic molecules (e.g. sucrose) to pass easily between cells.
Few organelles (no nucleus, little cytoplasm) reduce resistance to flow.
Companion cells provide ATP and proteins needed for active transport and support sieve tube elements.
27
What is meant by the terms "source" and "sink" in translocation?
Source: The region where sugars (mainly sucrose) are produced during photosynthesis (e.g., leaves).
Sink: The region where sugars are used or stored (e.g., roots, growing tissues, fruits).
28
Can a source and sink change in a plant?
Yes, depending on the season or growth stage. For example:
In spring, stored sugars in roots (sink) become a source as they are transported to growing shoots (sink).
In summer, leaves act as a source, supplying sugars to developing fruits (sink).
29
What substances are transported in the phloem?
Sucrose (main transport sugar, as it is less reactive than glucose).
Amino acids (for protein synthesis).
Inorganic ions (e.g., potassium, phosphate, magnesium for metabolism).
30
Why can't translocation be explained by diffusion alone?
Because the rate of movement in the phloem is too fast for simple diffusion. Instead, it is explained by the Mass Flow Theory.
31
What are the full three phases of the mass flow hypothesis
Loading at the source:
Sucrose is actively transported from companion cells into sieve tube elements using ATP, which lowers the water potential inside the sieve tubes.
Water enters from the xylem by osmosis, increasing the hydrostatic pressure.
Mass flow through the phloem:
The high pressure at the source pushes sucrose through the phloem towards areas of lower pressure — from source to sink — down a pressure gradient.
Unloading at the sink:
Sucrose is removed from the sieve tubes into sink cells (e.g. roots or storage tissues), which increases the water potential inside the sieve tubes.
Water moves out of the sieve tubes by osmosis, lowering the pressure at the sink end.
32
How is sucrose loaded into the phloem? Stage one
Sucrose travels down a concentration gradient from photosythesising cells to companion cells
Hydrogen ions (H⁺) are actively transported from companion cells into cell walls using ATP.
These H⁺ ions diffuse down a concentration gradient through carrier proteins into sieve tubes elements
Sucrose molecules are transported with hydrogen through co transport
33
What causes the movement of sucrose through the sieve tubes(mass flow through phloem stage 2)
The sucrose that is transported to sieve tube by photosynthesising cells (source)
causes the water potential in sieve tube elements to decrease Water moves into sieve tube elements by osmosis from the xylem
This increases hydrostatic pressure with in them
At the respiring cells sucrose is used for storage or respiration so they have a low concentration of sucrose , so sucrose actively transported from sieve tube to these respiring cells (sinks) which lowers their water potential ,water moves in by osmosis from sieve tubes decreasing hydrostatic Pressure in sieve tubes
The high hydrostatic pressure at the source and low one at the sink causes a mass flow of sucrose solution down this hydrostatic gradient in the sieve tubes
34
How is sucrose removed at the sink?stage 3
Sucrose is actively transported out of sieve tubes into sink cells (e.g., root cells or storage organs).
35
Why does sucrose move from source to sink?
Because of the hydrostatic pressure gradient—high at the source and low at the sink.
36
Is mass flow a passive process?
The movement of sucrose through the phloem is passive, but the loading and unloading of sucrose require ATP, making the overall process active.
37
What is the setup of a ringing experiment
A circular ring of bark (including phloem) is removed from the entire circumference of a stem.
The xylem is left untouched to allow water movement to continue.
The plant is left for some time to observe changes above and below the ring.
38
What is a ringing experiment?
A method used to show that phloem is responsible for translocation, by removing a ring of bark and phloem from a woody stem and observing the effects.
39
What happens above and below the ring after a period of time?
Above the ring → A swelling forms due to build up of sugars.
✖ Below the ring → Tissues die due to a lack of sugar transport to the lower regions.
40
Q: What happens if radioactive tracers (e.g., carbon-14 labeled sugars) are used?
Plants are grown in an atmosphere containing radioactive carbon dioxide (¹⁴CO₂). During photosynthesis, the ¹⁴C isotope is incorporated into sugars. As these radioactive sugars move through the plant, thin stem sections are placed on X-ray film (autoradiography). The film blackens where radiation from the ¹⁴C is detected. These blackened areas correspond to the location of phloem tissue, showing that sugars move through the phloem. Tissues that do not blacken the film do not transport sugars, proving phloem is responsible for translocation.
41
What does the ringing experiment demonstrate about translocation?
Sugars move in the phloem, not the xylem.
The phloem is responsible for translocation, as sugars accumulate above the removed ring.
Tissues below the ring die due to lack of sugars for respiration and growth
42
How are tracer experiments used to track the movement of sugars in plants?
Plants are exposed to radioactively labeled carbon dioxide (¹⁴CO₂).
This ¹⁴C is incorporated into sugars during photosynthesis.
The movement of these radioactive sugars through the plant is tracked over time.
43
How is the movement of radioactive sugars detected
Autoradiography is used:
Plant stems are cut into cross-sections and placed on photographic film.
The film blackens where radioactive sugar is present, showing movement in the phloem.
44
What are two key pieces of evidence that organic molecules move through the phloem?
Aphid experiments: When aphids feed on phloem sap, sugary liquid flows out, showing that organic molecules are transported in the phloem under positive pressure.
Radioactive tracer experiments: Plants given radioactive CO₂ produce ¹⁴C-labelled sugars, which are later detected in the phloem only, proving sugars move through the phloem — not the xylem
45
What are aphids, and how are they used in phloem studies?
Aphids are insects that feed on plant sap using needle-like mouthparts called stylets.
Their stylets penetrate the phloem, allowing scientists to extract phloem contents.
46
What do aphid experiments show about sugar movement?
The sugar content in phloem is higher near the source (e.g., leaves) and lower at the sink (e.g., roots).
This confirms movement of sugars from source to sink via phloem.
47
What are the purposes of mitosis
Replace dead/damaged cells.
Growth: Increases the number of genetically identical cells so organisms can grow.
Asexual reproduction: Produces genetically identical offspring
48
What is the outcome of mitosis?
Two genetically identical daughter cells.
49
What are the three main stages of the cell cycle?
Interphase (G1, S, G2)
Mitosis (Prophase, Metaphase, Anaphase, Telophase)
Cytokinesis
50
What happens during interphase?
G1 Phase (Gap 1): Cell grows, proteins and organelles are made.
S Phase (Synthesis): DNA semi conservative replication occurs so each chromosome has two identical sister chromatids.
G2 Phase (Gap 2): The cell produces RNA, histones, ATP, enzymes, and other molecules needed for mitosis.
51
Why is interphase important?
It ensures the cell is ready for division by replicating its DNA and preparing organelles
52
What happens to chromosomes during interphase? Why are they not visible under microscope
Each chromosome is duplicated, forming sister chromatids joined by a centromere.
Chromosomes are not visible under the microscope in interphase because they are in a loose chromatin state.
53
What happens at the end of G2?
In preparation for mitosis centrioles mature and migrate to ethier part of cell
54
What would happen if a mutation occurred during S-phase?
The mutation would be copied into both daughter cells, potentially causing cancer or genetic disorders.
55
What happens during prophase?
Chromosomes begin to shorten and thicken ,coils form visible chromosome structure and the nuclear membrane disappears
56
What happens during metaphase?
Chromosomes align at the equator (middle) of the cell.
Centrioles produce Spindle fibers attach to the centromere of each chromosome
57
What happens during anaphase?
Spindle fibers contract, pulling sister chromatids apart towards opposite poles.
Centromeres split
58
What happens during telophase?
Chromatids uncoil back into chromatin.
Nuclear envelope reforms around each new nucleus.
Cell membrane starts to fold forwards at the equator which is called a cleavage line
59
What is cytokinesis?
The division of the cytoplasm, resulting in two genetically identical daughter cells.
60
How does cytokinesis differ in plant and animal cells?
Animal cells: Cleavage furrow forms, splitting the membrane.
Plant cells: A cell plate forms, developing into a new cell wall.
61
What is the mitotic index?
Mitotic Index=
Total number of cells visible/
Number of cells undergoing mitosis visble
62
What does a high mitotic index indicate?
Rapid cell division (e.g., in growing tissues or tumors).
If too high, it may indicate cancer cells dividing uncontrollably.
63
How does cancer develop?
Mutations occur in genes that control cell division.
This leads to uncontrolled mitosis, forming a tumor.
Rate of cell multiplication is faster than the rate of cell death
64
How do cancer treatments work?
A: By disrupting the cell cycle, preventing cancer cells from dividing.
65
Name two types of cancer drugs and their mechanisms.
Cisplatin → Prevents DNA replication, stopping the S-phase of the cell cycle.
Vinca Alkaloids → Disrupt spindle formation, preventing mitosis (M-phase).
66
Q: Why do chemotherapy drugs also affect normal cells?
Cancer drugs target rapidly dividing cells, so they also affect fast-dividing healthy cells.
This includes hair follicle cells, which is why hair loss is a common side effect.
67
How can we prove xylem has negative pressure
When a xylem vessel is cut, air is drawn in instead of water leaking out. This shows the pressure inside is lower than atmospheric pressure, proving the xylem is under tension (negative pressure).
68
Why in the ringing experiment is there swelling above the ring
Phloem is removed, so sucrose can’t move down past the ring.
Sucrose continues to be made in the leaves (source) and gets transported downward.
Since it can’t pass the cut, it accumulates above the ring, increasing osmotic pressure, which draws in water.
This causes a swelling where the sugars collect.
69
What evidence supports the mass flow hypothesis in plants?
Pressure exists in sieve tubes (sap released when cut).
Higher sucrose concentration in leaves (source) than in roots (sink).
Downward phloem flow occurs in daylight but stops in darkness or shade.
Increases in leaf sucrose are followed by increases in phloem sucrose.
Metabolic poisons/lack of oxygen inhibit sucrose translocation.
Companion cells have many mitochondria and produce ATP.
70
What evidence challenges the mass flow hypothesis in plants?
Sieve plates may hinder flow; their exact function is unclear.
Not all solutes move at the same speed (they should if mass flow was correct).
Sucrose is delivered at similar rates to all regions, not faster to low-concentration areas as theory predicts.
71
Lysogenic full cycle
Virus attached to cell its invading using attachment proteins
Lipid envelope fuses with cell membrane genetic material enters cell
Using RNA nucleotides RNA replicates
RNA holds info on how to construct protein Capsid and attachment proteins
Cell does translation and constructs viruses proteins
Reconstruction of viruses using host cell
Pinches off and leaves cell using cell membrane to form lipid envelope
Eventually cell burst
72
Binary fission
Circular dna replicates both copies attach to cell membrane
Plasmids replicate
Cell membrane grows between the 2 dna and pinches inward dividing cytoplasm into 2
New cell wall forms
2 identical cells formed with single copy of circular dna and variable number of plasmids
73
Define classification
Organisation of living organisms into groups ,this is non random
74
What system do we use to name species
Binomial
75
All the features of the binomial system
Universal based on Latin/greek names
First name is the generic name it denotes the genus(group of species that are closely related)to which the organism belongs to
Second name is the specific name which shows what species organism belongs to
76
What are the rules applied to the binomial system
Names must be written in italics or underlined to show they are scientific names
First letter of generic name is capital specific name is lower case
If specific name is not know it can be written as sp
77
What does courtshape (actions behaviours that help animals find a mate) behaviour help animals to do
Help animals mate by..
Recognising own specie so that breeding only occurs in species to produce fertile offspring
Identify a partner that is sexually mature to breed and fertile , males will use courtshape behaviour to find this out based on how female responds
Form a pair bond that will lead to successful mating
Align mating so it takes place when there is max probability of egg and sperm meeting
Become able to breed-bring member into physiological state to breed
78
What is the theory and practice of biological classification called
Taxonomy
79
What is artificial classification
Artificial classification is a way of grouping organisms based on observable physical features (like size, shape, or colour), not based on evolutionary relationships, does not show genetic or evolutionary links between organisms
Quick and easy but not accurate scientifically
80
Phylogenetic classification
Based on evolutnary relationships between organisms and ancestors
Classifies species into groups based on shared features derived from ancestors
Arranges groups into hierarchy in which the groups are contained in larger composite groups with no overlaps between groups
81
Dif between artificial and phylogenetic classification
Artificial classification groups organisms by observable features (e.g., size, colour), not by ancestry.
It can group unrelated organisms if they look similar, so there is overlap
Phylogenetic classification groups organisms by evolutionary relationships (common ancestors, DNA, fossils).
No overlaps in phylogenetic classification — each organism fits clearly based on ancestry.
82
Define species and what shows a single species
Basic unit of classification ,members of a single species are capable of breeding to produce fertile offspring
83
What is a taxon?
A taxon is a group within a phylogenetic biological classification
84
What is taxonomy
Taxonomy is the study of classifying organisms into groups based on evolutionary relationships.
85
What are the three domains
Bacteria, Archaea, and Eukarya
86
Taxonomic ranks
Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
87
Archaea domain
Singles celled prokaryotes that were originally classified as bacteria due to physical appearance
But they are not the same as..
Their genes and protein synthesis is more similar to eukaryotes
Cell em membranes contain glycerol attached to fatty acids by ether linkage
No murein in cell wall
They have more complex form of rna polymerase
88
Eukarya domain
Groups of organisms made up of one or more eukaryotic cells
Cells posses membrane bound organelles such as chloroplasts and mitochondria
Memebranes containing fatty acids chains attached to glycerol by ester bonds
Not all posses cell wall but when does no Murein
80s ribosomes wcih is larger than bacteria and archaea
89
What are the four kingdoms in the domain Eukarya?
Protoctista, Fungi, Plantae, Animalia
90
What does a phylogenetic tree show
Evolutionary relationships and common ancestors between species.
91
What does the closeness of branches on a phylogenetic tree represent?
How closely species and ancestors are related
92
Define species diversity
The number of different species and the number of individuals in a species in a community
93
What will be bacteria domain(domain is highest group)
Single celled prokaryotes
Absence or membrane bound organelles like nucleus mitochondria
Unicellular -made of one cells
Ribosomes are 70s which is smaller than eukaryotes (80s)
Cell walls made or murein are present (never chitin or cellulose)
Single loop of makes dna made of nucleic acids but no histones
94
What three components does biodiversity include
Specific diversity
Genetic diversity
Ecosystem diversity
95
Define genetic diversity
Variety of genes that make up individuals of a species that make up the population
96
Define ecosystem diversity
Range of different habitats from one local habitat to the whole earth
97
What is a measure of biodiversity
Species richness
Number of different species in an area at a given time
98
Can two communities have the same species richness but different diversity
Yes. They may have the same number of species, but different proportions of individuals in each species
99
What does biodiversity index reflect and what does it represent when high
Reflection of number of species and abundance of species in an area
When its high the more stable the ecosystem so usually less effected by change
100
Explain why an increase in greenhouse gases is more likely to result in damage to communities with a low species diversity index than communities with a high index.
Communities with low species diversity have fewer species, so there is less genetic variation
If environmental conditions change (e.g. due to greenhouse gases), it's more likely that all or most species will be affected.
This means there's less chance that any species will survive and maintain the ecosystem.
In contrast, high diversity communities have more species, so more genetic variation so it's more likely that some will survive and maintain ecosystem functions.
101
Why do agricultural ecosystems have lower species diversity than natural ecosystems?
Farmers often grow one species (monoculture) and remove other species to maximise yield
102
What happens to the genetic variety in agricultural species
It is reduced to only a few alleles that give desirable traits.
103
How does biomass relate to reduced diversity in farming?
Most biomass is taken up by the one desirable species, leaving less space and resources for others
104
Why do other species struggle to survive in farmland ecosystems?
They face more competition for limited resources and are often killed by pesticides
105
State the practices that have DIRECTLY removed habitats and deacreased species diversity
Remnoval of hedgerows and grubbing out woodland
Creating monolocutures e.g replacing natural meadows with cereal crops or grass
Filling in ponds and draining marsh and other wetland
Over grazing land, e.g to many sheep prevent regeneration of woodland
106
Indirect actions reducing species diversity and removed habitats
Use of pesticides and inorganic fertilisers
Escape of effluent from sillage stores and slurry tanks into water courses
Absence of crop rotation lack of intercropping or under sowing
107
What are the management techniques that can be used to increase species and habitat diversity without raising food costs and getting lower yield
Plant and maintain hedgerows
→ Support nesting sites and wildlife corridors.
Leave field margins and wet corners
→ Provide habitats for insects, birds, and plants without affecting crop production.
Maintain/create ponds
→ Support aquatic biodiversity.
Reduce pesticide use
→ Encourages natural predators and pollinators.
Use organic fertilisers / crop rotation
→ Maintains soil health and supports diverse organisms.
Use intercropping
→ Naturally controls pests and reduces herbicide use.
Create hay meadows instead of silage fields
→ Allows wildflowers to grow and reseed.
108
What determains observable characteristic of organisms
Genes
Environmental factors
109
What are the limitations of using observable characteristics to measure genetic diversity
Lots of traits are polygenic (controlled by multiple genes)
Charactertics often show continuous variation
Environment effects charactertics
Hard to determain what is effected by environment vs genes
110
What method has replaced observing characteristics for comparing genetic diversity
DNA base sequence analysis, made possible by gene sequencing technologies.
111
How is DNA base sequence comparison used to assess genetic diversity?
DNA sequencing determines the exact order of nucleotides in DNA.
The more similar the base sequences between individuals/species, the more closely related they are.
112
How is mRNA used to measure genetic diversity?
mRNA base sequences are complementary to DNA and reflect the genes being expressed, so comparing mRNA sequences helps assess genetic differences.
113
How can amino acid sequences be used to assess relatedness between species?
Because DNA determines proteins, comparing base sequences reveals genetic differences. The more similar the DNA, the more closely related the organisms.
