9.1- chemical control

Question 1

what does homeostasis mean?

Answer 1

-maintenance of a constant internal environment
-in humans out internal environment is made up of fluid surrounding our cells, features of this fluid must remain constant
-involves constant changes around an optimum point

Question 2

3 things which can fluctuate in order to keep homeostasis

Answer 2

1. temp
2. pH
3. water potential

Question 3

importance of homeostasis; temp and pH

Answer 3

-changes in pH and temp effect proteins e.g. enzymes+ channel proteins
-changes can cause reduction in rate of reaction (reduced kinetic energy) or denaturation
-

Question 4

importance of homeostasis; water potential

Answer 4

-changes in water potential of tissue fluid or blood can cause a change in volume of cells due to osmosis
-particularly influenced by glucose conc which effects respiration

Question 5

4 factors of the control mechanism

Answer 5

1.optimum- point at which reaction works best
2.receptor- detects change from optimum
3.coordinator- links receptor and effector
4.effector- muscle or gland which brings changes to return to optimum

Question 6

what is negative feedback?

Answer 6

-system deviates from optimum
-change is detected by reeptor
-change is produced which returns system back, closer to optimum

Question 7

what is positive feedback?

Answer 7

-system deviates from optimum
-change detected by receptor
-change then produced which causes an even greater deviation from optimum
-e.g. oxytocin makes uterus contract harder, baby pushes against and stretches cervix, more released

Question 8

endocrine glands and hormones

Answer 8

-hormones are organic chemicals produced in an endocrine gland
-they travel in blood and can be widespread or targeted
-protein or peptide hormone examples are insulin, ADH
-steroid hormone examples are oestrogen and progesterone

Question 9

hormone release systems

Answer 9

-endocrine glands can be stimulated to release hormones by nerves or other hormones
-pituitary gland often secretes hormones which affect other glands

Question 10

how is the pituitary gland linked to hypothalamus?

Answer 10

-both located in brain
-hypothalamus often controls pituitary

Question 11

how does the hypothalamus control the pituitary gland?

Answer 11

-hyp contains neurosecretory cells which produce secretions from axons
-group of these cells called neurosecretory cells 1 produce substances that stimulate or inhibit release of hormones from anterior pituitary
-they are known as releasing factors or release inhibiting factors
-Neurosecretory cells 2 produce secretions that are stored in the posterior pituitary and released later as hormones

Question 12

all about pituitary gland

Answer 12

-controlled by hypothalamus
-produces 6 hormones from anterior lobe e.g. GH or TSH
-produces 2 from posterior lobe e.g. oxytocin and ADH

Question 13

hormone mode 1- release of second messenger

Answer 13

-hormone binds to receptor on target cell membrane- may do this as they are not lipid soluble and cannot cross membrane
-triggers intracellular membrane bound reactions
-stimulates release of second messenger
-second messenger activates enzymes to alter metabolism of cell

Question 14

example of second messenger

Answer 14

1.adrenaline binds to receptor
2.this activates enzyme called adenyl cyclase which converts ATP to cyclic AMP
3.cAMP acts as second messenger
4.it triggers diff responses in cell e.g. inc respiration and muscle contraction

Question 15

exam q- Adrenaline binds to receptors in the plasma membranes of liver cells. Explain how this causes the blood glucose concentration to increase.

Answer 15

• Adenylate cyclase activated / cAMP
  produced /
  -activates enzymes in cell
  -(So) glycogenolysis / gluconeogenesis
  occurs / glycogenesis inhibited;

Question 16

hormone mode 2- hormone enters cell

Answer 16

-hormones pass through membrane and bind to receptor inside the cell
-They form a hormone-receptor complex which passes into the nucleus and acts as a transcription factor to regulate gene expression.

Question 17

what is a tropism?

Answer 17

-growth in part of a plant in response to directional stimulus
-plant either grows towards or away from stimuli
-

Question 18

3 types of tropisms

Answer 18

-phototropism
-gravitropism
-hydrotropism
-all usually involve plant growth factors

Question 19

how do plants grow?

Answer 19

-cell division occurs in meristem tissues (roots and shoots)
-these areas are influenced by plant hormones
-examples are auxins, cytokines and gibberellins

Question 20

all about auxins

Answer 20

-produced in young shoots
-move down the roots
-movement involves some active transport and calcium ions
-apical dominance= supress growth of lateral shoots so main stem can grow fastest
-promoting root growth
-Tropic response of plant shoots to unilateral light

Question 21

how IAA works in steps

Answer 21

1.cells in shoot tip produce IAA
2.IAA diffuses back down to zone of elongation
3.IAA molecules bind to specific receptor sites on membrane, activating pumping of H+ ions into cell wall spaces
4.this changes pH to 5 (optimum for enzyme) which break bonds between cellulose and myofibrils
5. cells absorb more water by osmosis causing cell walls to stretch and therefore elongate and expand

Question 22

auxins- why do shoots grow towards light?

Answer 22

-when exposed to light from one direction, the auxins diffuse to the unilluminated side
-this means greater conc of auxins in zone of elongation on dark side
-stimulates these cells to grow so shoot grows towards light
-transport becomes asymmetric and the shoot continues to grow towards the light.

Question 23

roles of gibberellins

Answer 23

-growth regulators
-stimulate elongation of growing cells
-promote fruit growth
-break dormancy of seeds
-stimulate formation of enzymes in germination
-stimulate bolting

Question 24

role of gibberellins in seed germination

Answer 24

1.seed absorbs water and swells- embryo activated
2.embryo secretes gibberellin that diffuses to aleurone layer
3.gibberelin stimulates aleurone to produce amylase that diffuses into endosperm and breaks down food stores to provide embryo with materials for respiration and growth
4. enzymes digest endosperm, products released from endosperm are used by embryo to make new cells and germinate

Question 25

roles of cytokinins

Answer 25

-promote cell division in apical meristems (roots and shoots) and cambium (layer containing undifferentiated cells)
-promote lateral bud development
-work with ethene in abscission i.e. natural removal of leaves flowers and fruits

Question 26

what are phytochromes?

Answer 26

-blue/ green pigment in plants which exists in 2 forms
1.Pr (P660)- biologically inactive form which absorbs red light
2.Pfr (P730)- biologically active form which absorbs far red light

Question 27

conversion of phytochromes

Answer 27

-when one absorbs light it is reversibly converted to the other
-when Pr absorbs red light, it is converted to Pfr
-when Pfr absorbs far red light, it is converted back into Pr
-in absense of red light, Pfr gradually converts back to Pr

Question 28

speed of conversion depends on light instensity meaning…

Answer 28

-in low intensity, conversion takes mins
-in high it takes seconds
-in dark, Pfr converted to Pr very slowly but Pr is converted back

Question 29

phytochromes and growth

Answer 29

-during day, levels of Pfr rise
-sunlight contains more wavelengths 660nm (red light) than 730 (fr) so comversion of Pr to Pfr occurs more rapidly in day time than Pfr to Pr
-during night Pr levels rise
-red light wavelengths are not available, Pfr converts slowly back to Pr

Question 30

phytochromes and flowering

Answer 30

-different effects on flowering plants
-in LDPs Pfr stimulates flowering
-in SDPs Pfr inhibits flowering
-in DNPs they have diff flowering triggers, equal day and night lengths in tropical regions

Question 31

what is photomorphogenesis?

Answer 31

-process by which plant development is controlled by levels and type of light

Question 32

phytochromes and seeds

Answer 32

-when a seed germinates under ground the plant becomes etiolated, this means they grow rapidly, using up food resources and as a result become tall and thin
-this process is controlled by phytochromes

Question 33

how germination links to photomorphogenesis

Answer 33

-when seed emerges from underground, it contains Pr as it has not been exposed to light yet
-emerging seedling will show characteristics of etiolation

Question 34

characteristics of etiolation in seedlings

Answer 34

-rapid stem lengthening but little thickening to grow as tall as possible to reach light
-little root growth as needs just enough to anchor and obtain water
-no leaf growth so no energy wasted
-no chlorophyll so seedling remains white or yellow so no energy wasted by producing chlorophyll

Question 35

what changes occur once the tip breaks through surface soil?

Answer 35

-elongation of stem slows down
-stem straightens
-first leaves open
-chlorophyll forms and seedlings begin to photosynthesise

-all controlled by phytochrome interconversion

Question 36

how phytochromes work in soil

Answer 36

-internodes grow
-seed has plenty of Pr but no Pfr so no leaves or chlorophyll forms

Question 37

how phytochromes work in light

Answer 37

-Pr is rapidly converted to Pfr
-causes lengthening of internodes and leaves begin to develop
-chlorophyll produced

Question 38

phytochromes as transcription factors

Answer 38

-involved in switching genes on and off in nuclei of plant cells