Topic 4 Flashcards

Question

Why is the sclerenchyma a specialised cell for plant growth

Answer 1

- forms colours - stiffens the cell which provides support

Answer 2

-dead cells become Lined with lignin -all cell organelles leave as they are dead - this leaves a hollow tube with no organelles - so water an easily flow through -ligin makes it waterproof - so doesn’t leak out

Answer 3

Prokaryotes- no nucleus, large , DNA free , small ribosomes 70s Eukaryotes - has nucleus, large , dna packed in nucleus , large 80 ribosomes

Answer 4

- xylem vessels are fluid filled tubes -water moves upwards from root to shoot

Answer 5

Water vapour diffuses out through the stroma down a diffusion gradient - Water evaporates from the surfaces of cells lining the substomatal cavity - Water is replaced by means of capillary action within the cell walls. - Water is drawn out of the xylem - A continuous column of water is drawn up through xylem - Water evaporating in this way is known as transpiration - The stream of water passing through the plant is known as the transpiration stream

Answer 6

- water is under tension as its pulled up the plants -lignification of the xylem walls prevents them from collapsing - the water colum does not break when it’s pulled due to the cohesive forces between water molecules as a result of H bonding Water in narrow tubes sticks together very strongly - The movement of water through the xylem provides a mass flow system for the transport of inorganic ions - These are absorbed into the roots and are required throughout the plant

Answer 7

-Develops from a column of long, narrow cells in the growing stem - Phloem cells are alive whereas xylem vessels are dead. - The nucleus and most cell contents disintegrate during development - Only a few organelles remaining in thin layer of cytoplasm close to the cell wall - The end walls of each sieve tube cell contains holes that are aligned with neighbouring cell to allow transfer of material - Perforated end walls are called sieve plates - The section of a phloem sieve tube between sieve plates is called the sieve tube element - The lumen is continuous through the sieve plates at each end of the

Answer 8

Main substances transported are usually sucrose and amino acids - Produced in the leaves by photosynthesis - The fluid in the lumen moves along the sieve tube - In some sieve tubes the fluid flows from the leaves down to the roots - Where some sugars and amino acids are used for growth - And sugars may be used as a source of energy or converted to polysaccharide (such as starch) and stored. - In other cases it may move from the leaves to the buds, developing flowers, and fruits and the seeds

Answer 9

- found in phloem alongside a sieve tube -They still have have nucleus, mitochondria, ribosomes and RER - These cells perform the metabolic functions that maintain the sieve tube

Answer 10

- complete full cell - with its cell contests pressing out on cell wall

Answer 11

- Animal and laboratory studies on isolated cells and tissue cultures - In order to assess the safety - And determine the effectiveness

Answer 12

-Small group of healthy volunteers - Are given in different dosages - Used to determine whether or not the drug acts as it is predicted in lab tests

Answer 13

- small group of volunteers with the disease - Are treated to test the drugs effectivess

Answer 14

-Large group of patients are selected and divided randomly into two groups - One group is given the compound being investigated - The second is given a placebo - Neither the patients nor doctors know who has been given the drug or not

Answer 15

- protect their embryo -aid dispersal - provide nutrition for new plant

Answer 16

- Burning fossil fuels contributes to a net increase in atmospheric CO2 which contributes to climate change - Oil reserves will eventually run out - Plastics generate non-biodegradable waste, creating waste disposal problems

Answer 17

- take in endangered animals to breed - they Increase the number of individuals of the species to prevent extinction - Maintain genetic diversity within the captive population - Reintroduce animals into the wild

Answer 18

In small populations whether in the wild or in captivity - The likelihood of closely-related individuals mating increases - This inbreeding causes the frequency of homozygous genotypes to rise - Due to loss of heterozygotes - Inbreeding results in individual inheriting recessive alleles from both parents and the accumulation of the homozygous recessive genotypes in the offspring - Many recessive alleles have harmful effects - So an inbreeding depression occurs - The offspring will therefore be less likely to survive reproduce

Answer 19

- on sight - best way to prevent genetic drift and interbreeding depression

Answer 20

- off sight -can play a role in preventing genetic drift and interbreeding depression

Answer 21

- Shows the history and location of all the species - In the places that co-operating in an overall breeding plan - Used to ensure that genes from all of the founder members of the population are retained - And equally represented in the subsequent generation. - This requires that individuals that breed poorly in captivity must be encouraged to breed - Whilst those that are particularly good must be limited

Answer 22

- As plants are threatened by habitat destruction, climate change and over-harvesting - Seed banks are an ex-situ form of conservation - Small samples of seeds are taken - They are stored easily due to their small size and ease of storage - They are kept in dry and cool conditions - After a month a sample is taken and germinated on agar plates - To make sure that the seeds are still alive - If germination rate falls below 75% then the seeds will be grown - New seed samples will then be taken