Biology A Level- Chapter 15 Control and Coordination Part 2 (Muscle Contraction, Plant Coordination)

1. Muscle Contraction
• Contraction of striated muscles; only contract
when stimulated by impulses that arrive
(neurogenic)
• Different with cardiac and smooth muscles
• *refer to Table 15.2 Pg.407

3. The Structure of Striated Muscles
• One bicep contains of thousands of mucle
fibres.
• Highly specialised cell with organised
contractile proteins in the cytoplasm
forming a multinucleate muscle fibre
• Sarcolemma- Cell surface membrane
• Sarcoplasm- Cytoplasm
• Sarcoplasmic Reticulum (SR)- Endoplasmic
reticulum

4. • Deep infoldings in the sarcolemma forming
the transverse system tubules (T-tubule)
• Membranes of SR have high number of
protein pumps; transport calcium ions ino the
lumen (cisternae) of SR
• High number of mitochondria; packed tightly
between myofibrils  aerobic respiration to
generate ATPs

5. • Striations on muscle fibre- Myofibrils
-striped in same way and lined up
-made up of thick and thin filaments
• Thick filaments are made up of myosin
• Thin filaments are made mostly of actin

6. Structure of a Muscle

7. Structure of Muscle Fibre

9. • I band = only thin filaments (lighter part)
• A band = overlap of thick and thin filaments
(darkest part)
• H band = only thick filament present
• Z line= attachments of actin filaments
• M line = attachments of myosin filaments
• Sarcomere = part between Z line
-z-line shaped as Z-disc as the myofibrils are
packed into cylindrical shape.

11. The Structure of Thick and Thin
Filaments
• Thick filaments; made up of myosin (fibrous
protein with globular head)
-lie together in in bundle (M-line)
-globular heads are pointing away from M-line
• Thin filaments; made up of actin (globular
protein)
-chain of actin molecules are twisted, forming the
filament
-tropomyosin twisted together with actin
-troponin attached to the actin at intervals

12. Structure of one sarcomere

14. Muscle Contraction
• Sliding filament model; the movement of
muscle
-movement generated by contraction
-the sarcomere in each myofibril get shorter as
the Z discs get pulled closer
• Energy for the movement coming from ATPs
attached to the myosin heads
*each myosin head is ATPase

15. When muscle contracting..
1. Calcium ions are released from SR, get bind
to troponin; troponin gets to change the
shape.
2. Troponin and tropomyosin move to different
position on the thin filaments;
-exposing the actin-binding site to myosin
-forming cross-bridges between thin and
thick filaments

16. 3. Myosin heads move; pulling the actin filaments
to the centre of sarcomere (H band become
shorter)
4. Myosin head hdyrolyse the ATP, provide energy
for the head to release the actin
-the heads move back to the previous position and
bind again to the exposed site of actin
5. Thin filaments moves due the previous stroke
-myosin head bind to actin further, closer to the Z-
disc

17. • The myosin head moves again, pulling the
actin filaments even further; hydrolyse more
ATPs to repeat the process
• Can continue as long as the troponin and
tropomyosin active sites are not blocked, and
the ATPs are supplied

18. Control and Coordination in
Plants

19. Control and Coordination in Plants
• Responds to the factors like gravity, light and
water availability, in changing the growth
• The responses are done by quick changes in
turgidity, such stomata respond to changes in
changes in humidity, carbon dioxide
concentration and water availability.

20. Electrical Communication in Plants
• Plant action potentials are triggered when
membrane is depolarised (have the same way
of electrochemical gradient as animal cells)
• Some species, they have the response to the
stimuli coordinated by action potentials.
-Mimosa, respons to the tocuh by folding its
leaves

21. • Depolarisation of plants; results from the outflow
of negatively charged chloride ions Cl- (not from
the inlfux of positively charged Na+
• Repolarisation achieved in the same way by the
outflow of potassium ions, K+
• Plants do not have nerve cells but transmit the
electrical waves activity, same as along the
neurones in animals.
• Action potentials are trasmitted along the the cell
membrane of plant cells, from cell to cell through
plasmodesmata

23. • The action potentials generated last much longer
and travel slower than in animal neurones.
• Different stimuli can trigger the action potentials
of the plants.
-e.g dripping acid solution on soya bean plant
-Colorado beetle larvae feeding on potato leaves
• these action potentias are to coordinated
stress signals and damage signals.

24. Venus Fly Trap
• Dionaea muscipula;
carnivorous plant that obtain
nitrogen supply from small
animals (insects)
• Special structure of leaf divided
into 2 lobes;
-red coloured inside of the lobe
and secrete nectar to attracts
insects
• Each lobes has 3 stiff sensory
hair (respond if deflected)

25. • Outer edge of the lobes have stiff hair (thorn-
like) interlock to trap the insects when closed.
• The lobes surface have many gland that
secrete enzymes for the digestion.
touch stimuli on the sensory hair will
stimulate the action potential, causing the lobes
to fold and capture the insect

27. • Deflection of sensory hair activates the calcium
ion channels (at the base of the hair)
-the channels open, and influx of calcium will
trigger the receptor potential.
• If 2 of 3 hairs stimulated; or one hair is stimulated
twice within 20 – 35 sec., action potentials wil
travel across the trap.
• If second stimulus trigger outside from the
intervals (first stimulus), it will start as first again.
• Time between stimulus and response is 0.5s
-less than 0.3s taken to close and trap the insect

28. • To completely closed the trap, the leaf need
ongoing trigger of the hair (struggle movement of
the insects)
• Further stimulation of inner lobes will cause
influx of calcium ions into gland cells.
-exocytosis of enzyme-containing vesicles (same
way as synapse action)
• The leaf will be closed up to a week to complete
the digestion.
-cells of the upper surface of midrib grow slowly
and will reopen

29. • Adaptations of Venus fly trap:
1. One stimulus on single hair will not trigger
the closure.
2. The gaps between the stiff hairs, allow very
small insects to escape
-prevent waste energy of digesting small
insects

30. Chemical Communications in
Plants

31. Plant Growth Regulators
• Plant hormones are used to communicate
within the plantss.
• The hormones are released by a variety of
plant tissues (not by special glands by animals)
• They moves in plants by cell to cell (active
transport or diffusion); or transported through
phloem/xylem sap

32. Auxins
• Influent on growth aspects (including
elongation growth) which determines the
overall length of roots and shoots.
• IAA (indole 3-acetic acid) the principal
chemicals of auxin

33. • IAA is synthesised in the growing tips (meristems) of
shoots and roots
-transported back down the the shoot or up the root
by active transport from cell to cell, or lesser extent in
phloem sap
• Auxins stimulate cells to pump H+ ions (protons) into
the cell wall.
-become acidified, leads to loosening the bonds
between cellulose microfibrils and the matrix
surrounding them.
-The cell wall absorps water (osmosis); increase in
internal pressure cause the the walls to stretch and the
cells will elongate.

35. 1. Molecules of auxins bind to the receptor protein
(on cell surface membrane)
2. Stimulates ATPase proton pumps to move H+
ions from cytoplasm into the cell walls.
3. Protein (expansin) activated by the lowering of
pH
-loosening the bond between cellulose
microfibrils
4. Microfibrils move past each other, allowing the
cell to expand (with only little strength loss of
the cell wall)

36. Gibberellins
• Plant growth regulators synthesised in most parts
of the plants.
• High conc. in young leaves and seeds for the
growth process.
• Promotes different cell extension different with
auxins
-gibberellins stimulates the XET enzymes (in the
cell wall of stems)
-XET breaks the bond within the hemicellulose
molecules; cellulose microfibrils can moves apart
allowing for the extension.

37. • Gibberellins are involved in the controls of
germination of cereal seeds (wheat, barley)
• The seed is in dormant state when shed from the
parent plant: allows to survive the adverse
conditions (e.g only germinating when the
temperature rise)
• The seed contain embryo; which will grow to form
the new plant when germination occur
-embry is surrounded by endosperm; energy storage
of polysaccharide starch
-outer edge of endospermis aleurone, protein-rich
layer
-the seed itself is covered by tough, waterproof
protective layer

39. 1. Water uptakes initiates the germination
2. Embryo synthesise gibberellins
3. Aleurone layer synthesises amylase in
respond to gibberellins
4. amylase hydrolyses starch to maltose
5. Maltose is broken down to glucose and
tansferred to the embryo for respiration