Plant hormones, coordination and the brain

Question 1

What are plant growth factors and where are they produced?

Answer 1

Chemicals that regulate plant growth response to directional stimuli.
Produced in plant growing regions (apical meristems).
Diffuse from cell to cell / phloem mass transport.

Question 2

What is a phytochrome?

Answer 2

A plant photoreceptor with bilin chromophore group. Converts between biologically inactive Pr and biologically active Pfr.

Question 3

What effect does phytochrome have on plants?

Answer 3

They affect growth and development. They regulate aspects of development such as flowering and synthesis of chlorophyll.

Question 4

What is photomorphogenesis?

Answer 4

The pattern of plant growth and development determined by light intensity.

Question 5

How does phytochrome control photomorphogenesis?

Answer 5

Transition from Pr to Pfr controls localisation of proteins within cells, transcription of certain genes, phosphorylation of proteins.
It therefore affects germination, circadian rhythm and flowering.

Question 6

How does phytochrome control flowering?

Answer 6

Pr absorbs red light and converts to Pfr, which stimulates flowering (signifies that light intensity is great enough for photosynthesis)

Question 7

How does phytochrome affect gene transcription?

Answer 7

The Pfr can enter the nucleus where it can bind to transcription factors like PIF (phytochrome inhibiting factor) which activates the transcription of genes such as those involved in the synthesis of chloroplast proteins like RuBisCo.

Question 8

What is Indole Acetic Acid (IAA)?

Answer 8

A type of auxin which is mainly produced at growing plant tips which is used to promote cell growth and elongation.

Question 9

List the functions of auxins in plants

Answer 9

-Involved in trophic responses e.g. IAA
-Control cell elongation
-Suppress lateral buds to maintain apical dominance
-Promote root growth e.g. in rooting powders

Question 10

What is apical dominance?

Answer 10

When during the growth of the shoot, the growth of side shoots doesn’t take place. Maintained by the action of auxin, abscisic acid and cytokinins.

Question 11

How is germination stimulated?

Answer 11

1. Seed absorbs water, activating embryo to secrete gibberellins.
2. Gibberellins diffuse to aleurone layer, which produces amylase.
3. Amylase diffuses to endosperm layer to hydrolyse starch.
4. Hexose sugars act as respiratory substrate to produce ATP.

Question 12

How does IAA affect gene transcription?

Answer 12

Certain transcription factors related to auxin-controlled genes are in the nucleus. They’re typically blocked by other proteins from enhancing transcription. When auxin levels rise, these proteins are broken down and the transcription factors can promote transcription.

Question 13

Explain why shoots show positive phototropism.

Answer 13

1. Indoleactic acid diffuses to shaded side of shoot tip.
2. IAA diffuses down shaded side and causes active transport of H+ ions into cell wall.
3. Disruption of H-bonds between cellulose molecules and action of expansions make cells more permeable to water.
4. Cells on shaded side elongate faster due to higher turgor pressure.
5. Shoot bends towards the light.

Question 14

Explain why roots show positive gravitropism

Answer 14

1. Gravity causes IAA to accumulate on lower side of the root.
2. IAA inhibits elongation of root cells.
3. Cells on upper side of the root elongate faster, so the root tip bends downwards.

Question 15

What are gibberellins?

Answer 15

Plant hormones that control stem elongation, trigger the growth of the pollen tube during fertilization and stimulate the mobilization of food storage reserves during seed germination.

Question 16

List the functions of gibberellins.

Answer 16

Gibberellins stimulate:
-Germination
-Elongation at cell internodes
-Fruit growth
-Rapid growth/flowering

Question 17

What is the function of the cerebrum?

Answer 17

It’s responsible for all voluntary behavior, memory, personality, reasoning and learning.

Question 18

What is the function of each cerebral hemisphere?

Answer 18

Left hemisphere receives sensory information from the right side of the body and controls muscle coordination on the right and vice versa.

Question 19

What is the function of the cerebellum?

Answer 19

It controls muscle coordination and non-voluntary movement like balance and posture.

Question 20

What is the function of the hypothalamus?

Answer 20

It’s the control centre for the autonomic nervous system. It’s responsible for hormone production, regulation of the water potential of body fluids and control of behavioral patterns. It links the nervous and endocrine systems.

Question 21

What is the function of the medulla oblongata?

Answer 21

It regulates autonomic activities like ventilation, heart rate and peristalsis.

Question 22

Name 4 brain imaging techniques.

Answer 22

PET (Positron emission tomography) scans, MRIs, CT scans and functional MRIs.

Question 23

How does an MRI scan work?

Answer 23

It uses a magnetic field to cause protons from hydrogen atoms in water molecules to align. Radio waves then knock the protons out of alignment. Radio waves are turned off, the protons realign and emit radiation to receivers. The signal is used to produce a 3D cross-sectional image.

Question 24

Describe the advantage of using an MRI scan.

Answer 24

High resolution distinguishes tissues and provides more details than ultrasound or CT scans.

Question 25

How does an fMRI scan work?

Answer 25

It uses radio waves and a magnetic field to assess brain function through the visualization of blood flow in brain capillaries. It shows where most aerobic respiration occurs and changes in brain activity.

Question 26

How does a PET scan work?

Answer 26

A radioactive isotope like carbon with a short half-life is injected and used by the body to synthesize molecules. The isotope decays and emits gamma radiation to a detector. Active areas show higher radioactivity.

Question 27

What is a CT scan?

Answer 27

A medical imaging technique that uses specialized X-ray equipment and computer software to create detailed images of internal organs.

Question 28

What’s Parkinson’s disease?

Answer 28

A neurodegenerative disorder affecting movement and cognitive function.
There’s loss of dopaminergic neurons in cerebral cortex of the brain. It’s characterized by the formation of Lewy bodies.

Question 29

What causes Parkinson’s disease?

Answer 29

The death of dopamine producing cells within the basal ganglia and the midbrain. The exact cause of this cell death is unknown but it may be caused by a mix of environmental and genetic factors.

Question 30

Describe the link between serotonin and depression.

Answer 30

Low serotonin levels are correlated to depression. May be caused by low serotonin production, a problem with postsynaptic receptors or other linked variables. Evidence shows that drugs which increase serotonin levels in the synaptic cleft like selective serotonin reuptake inhibitors are effective treatments.