Detection of light in flowering plants

photoreception if the detection of light. this usually involves the absorption of light by a pigment known as a photoreceptor.
Light is important to plants because of the formation of chlorophyll, photosynthesis, initiates flowers, germniation and direction of growth.
Plants grown in dark condititons are said to be etiolated having yellow leaves, taller and thinner.
in the early stages of life this is an advantage as it can push through the soil more easily, faster growth to reach light wicker.

phytochrome is the photoreceptor, its a blue-green pigment present in small amounts in the leaves. it exists in two interconvertible forms Pfr and Pr.
Pr absorbs red light and is converted into Pfr, This is fast and is done in the light
Pfr absorbs far red light is converted into Pr, this is slow and is done in the dark
Pfr acts as a daylight length detector system.
Pfr promotes the flowering of long day plants
Pfr inhibits the flowering of short day plants


Germination:
seeds must take in water( IMBIBITION)
This causes the embryo to release gibberellic acid and this induces the synthesis of hydrolyic enzymes , including amylase.
Hydrolysis of starch takes place and it is broken down to maltose, this fuels respiration in the embryo so it an grow.

The Central Nervous System

this consists of the brain and spinal cord. it creates appropriate responses to sensory info.
the nervous system is first divided into the cns and the peripheral nervous system.
this consists of the crainial nerves.
brain parts:

cerebral hemisphere- 2 which make up the cerebrum, the largest part. connected by nerve fibres called the corpus callosum.
receives impulses from sensory receptors e.g. heat, cold, touch , sight, taste, smell
controls skeletal movements for voluntary movement
consciousness, memory, language, speech, emotions.

Hypothalamus-synthesis of hormone, osmoregulation and maintains body temperature.

Midbrain- conducts impulses between the hindbrain and forebrain, linked with visual and auditory reflexes.

cerebellum- acts with the cerebrum to produce skilled co ordinated movements, co ordinates balance and posture.

Pons-mainly nerve fibers joining the parts of the cerebrum, control of breathing.

Medulla Oblongata-controls rate and force of heartbeat, coughing, sneezing vomiting etc

The brain develops in the embryo from a neural plate.
fold arise and form a neural tube

3 main sections: forebrain contains: cerebrum and hypothalamus
midbrain contains: midbrain
Hindbrain contains: pons, cerebellum and medulla oblongata.


Spinal Cord- continuous with the medulla oblongata, there are 31 pairs of spinal nerves arise from the cord. It consists of a central area of Grey matter and an external layer of white matter. int he center is a central canal of fluid.
they grey is unmyelinated these neurone go to the skeletal muscles
the white matter are neurones going to the brain.

spinal reflexes: the effector neurone is stimulated by a neurone orginiating from the spinal cord.
a relay neruone links sensory and effector.

A reflex action is an immediate response to a sensory stimulus.
reflex arc:


withdrawal reflexes are for example moving rapidly away from a harmful simulus.
muscle stretch reflexes include two neruones sensory and effector. e.g knee jerk.

Nervous co-ordination

The nervous and endocrine systems work together to co ordinate the actions withing the body.

Nervous system:
info is passed as electrical impulses along nerve fibres and chemically over synapses.
Transmission is relatively rapid with a short response time. however it is short lived.
the response is very local as 1 nerve fibre supplies a group of effector cells.

endocrine systems:
info is passed as chemical substances in the bloodstream/plasma.
transmission is relatively slow and the response time is long, the response may carry on for a long time.
the response can be widespread and cells in different parts of the body can respond to the chemical.
cell body: contains the nucleus and mitochondria. providing atp for sodium/ potassium pump.
dendrites: increase the surface areas many synapses can be made with other neighboring neurones.
axon: transmit electrical impulses away from the cell body, they are long so there are fewer synapses to slow it down.
myelin: enclcoses the axon, fatty sheath. insulates, speeds up conduction and prevents action potentials being formed.
Nodes of ranvier: gap in the myelin sheath where action potentials can form.
synaptic bulbs: end of the branch the axon contains vesicles of neurotransmitters.

3 types of neurones:
1) sensory neurones- conduct nerve impulses away from a receptor toward the central nervous system.
2) relay neurones- conduct impulses from the sensory neurones to a motor neurone.
3)motor(effector) neurones conduct nerve impulses from a relay neurone in the spinal cord to an effector e.g a muscle.

myelination and schwann cells
schwann cells produce the fatty myelin surrounding the axon. the schwann cell wraps around the axon, covering it.
The action potentials move from each node of ranvier to the next.(saltatory conduction)
as the schwaan cell grows around the axon it twists many times and myelin is formed from the layers of schwaan cell membrane pressed together.

The Nerve Impulse:
potential differences are caused by uneven distribution of positively charged ions, on either side of the nerve cell membranes.
A resting potential exists when there is no nerve impulse.

outiside there is high Na+ and low k+
overall more positive outside = resting potential of -60mV
inside low Na= and high K
there is more k channel than na channels and 3na ions move out and 2 k move in .

Synapse:
in most synapses the gap is too large for electrical impulses to jump across and instead the impulse triggers the release of the chemical transmitter.

mechanisms for synaptic transmission
1) the action potential reaches the bulb of the presynaptic membrane, calcium channels open and calcium diffuses in.
2) calcium simulates the movement of vesicles to the membrane.
3) the vesicles fuse with the membrane and release their transmitter by exocytosis into the synaptic cleft.
4) the transmitter diffuses across and binds to receptors on the postsynaptic membrane, this causes ion channels to open.
5) the movement of ions results in the generation of a postsynaptic potential.
6) the transmitter substance is quickly broken down by enzymes.

Hormones in mammals

secreted by endocrine glands (into the blood capillaries).
are transported in blood plasma.
regulate changes in the internal environment
help homeostasis
may promote actions or inhibit effects
cause slow effects which are longer lasting.
affect a specific target organs

3 main groups:
1) amines: e.g. adrenaline from the medulla of adrenal glands.
2)peptides and proteins e.g. insulin and glucagon
3) steroids e.g. testosterone and oestrogen

released due to 1 of 3 types of stimulus:
1)presence or change in concentration of a substance
2) presence of change in concentration of another hormone
3) nervous stimulation e.g. adrenaline secreted from the adrenal medulla

hormone-------------site produced------------when-----------effect
insulin---------------beta cells-----------high glucose conc'-----reduced blood sugar
glucagon------------alpha cells----------low glucose in plasma---increases blood sugar
adrenaline----------adrenal meulla------nervous stimulation----incrse bld glucse & mre blood 2
ADH----hypothalamus-strd in pit gland--low blood water---increase water absorption in kidney
FSH--------anterior pit gland---------------------stims osestrogn and follicles in ovar develope
LH---------------pituitary---------------------------------stimulates ovulation
oestrogen----------ovary----------------menstrual cycle-----------stims endometirum
progesterone-----ovary---------------menstrual cycle-----------maintains endometrium
oxytocin-----------------------------during child birth--------stimulates contractions
prolactin---------ant pituitary---------after birth--------stims mammaries to produce milk


Endocrine: ductless gland

Exocrine: has a duct

Human eye

Light sensitive cells respond to the light resulting in action potentials being sent along the optic nerves to the visual cortex at the back of the cerebrum.

Key terms:

Conjuctiva- protective, thin layer of epithelial cells
Cornea- curved front of the eye, transparent and helps converge light rays
sclera: fibrous, outer protective structure.
choroid: supplies nutrients to all cells and removes waste, pigmented to prevent internal reflection. it has a network of blood cells.
Iris: muscular structure with an inner ring of circular muscle and an outer layer of radial muscle. it controls the amount of light entering the eye.
Pupil: hole in the middle of the iris where light continues into the eye
Vitreous humour: jelly like mass located behind the lens, it suspends the lensso it is not damaged.
Lens: transparent, flexible, curved structure. focus's incoming light onto the retina as it is refractive.
Retina: layer of sensory neurones, photoreceptors which respond to light. the rods and cones
Blind spot: this is where the bundle of sensory fibers form the optic nerve.
Uses of ATP: resynthesis of rhodopsin / sodium pump

A receptor is a cell or group of cells that detect a specific stimulus.

Rod cells:sensitive to light intensity. not sensitive to colour. they can respond to very dim light.
rhodopsin ---light---> opsin + retinal

Rhodopsin is stored in flattened membranous vesicles
low visual acuity in dim light.
opsin opens ions channels for the generation of action potentials.

Rod cells are absent in the fovea
The inner segments have lots of mitochondria which provide atop for the resynthesis of rhodopsin.
Rhodopsin is regenerated when there is no light. These are used at Night

a generator potential is produced which causes nerve impulses to be transmitted along a sensory neurone. Hyperpolarisation then depolarisation.
you have many 3/4 rods to one bipolar and ganglion cell.

around 120 million per retina

light hitting the pigment causes it to split.opsin iniates reaction ledin to the surafe becoming negative. Hyperpolarisation. When this reaches past a threshold, an action potential is stimulated in the sensory neruone. and this passes to the brain. this is to the visual cortex

Cone cells: require high light intensity to be stimulated. High visual acuity.
iodpsin----> photopsin + retinal
3 different types:
red-stimulated by red light
green- '' green light
blue- '' blue light
there are less cones than rods, and they are more focussed around and at the fovea.
Trichromatic theory states, colour vision is perceived according to the degree of stimulation of each type of cone.
1 cone cell is connected to 1 bipolar and ganglion cell.
6-7 million per retina.
Ganglion cell: transmitts action potential along neruones.
Bipolar cell:form an intermeidiate which connect photosensitive cells to ganglion cells.

Iris/pupil reflex:
the amount of light coming into the eye is detected by recpetors in the retina. reflex pathways lead to the circular and radial muscles of the iris contracting or relaxing.
High intensity light, leads to constricted pupils (small) circular muscle contract and radial relax.
low intensity light, leads to a dilated pupil (large) circular muscles relax and radial contract.

The creation of new glucose is GLUCONEOGENESIS

A rise in blood glucose concentration:
1) receptors pick up that there is high glucose in the blood
2) the beta cells in the islets of Langerhans secrete insulin directly into the blood stream.
3) insulin increases the permeability of of cell membranes to glucose , so more glucose is absorbed.
4) Insulin also activates the condensation of glucose to glycogen in glycogenesis
5) insulin also increases the rate of respiration of glucose.
6) blood glucose decreases


A decrease in blood glucose concentration:
1) alpha cells of the islets of Langerhans secrete glucagon into the blood stream.
2) this activates the hydrolysis of stored glycogen to glucose . this is called glycogenolysis
3) blood glucose increases

Pancreas:
key organ in controlling blood glucse levels
cells are known as the islets of langerhaans, are endocrine function.
Alpha cells secrete: glucagon
beta cells secret: insulin

these hormones are secreted straight into the blood capillaries
they are antagonistic

Insulin is a hormone that decreases the level of glucose in the blood. Two effects of insulin are cells are more permeable to glucose, speeds up acquisition. it also activates enzymes stimulation the conversion of glucose to glycogen.
Its main target organs are the Pancreas, Liver, muscles.

Glucagon hormone that increase blood sugar, main effect is that it activates enzymes which are responsible for converting glycogen into glucose (glycogenolysis)

the brain only respires glucose

glycogenesis: the synthesis of glycogen from glucose under the influence of insulin

glycogenolysis: the breakdown of insoluble glycogen under the influence of glucagon to form glucose.
gluconeogenesis: the creation of glucose from non carb sources e.g. lipids/ fatty acids or protein.

test for glucose:
diabur strips, yellow= no glucose,
progressively darkgreen-blue= glucose present

Benedicts test:(less sophisticated)
not specific to glucose just for redcuing sugars
after heating for 3 mins a blue solution means no glucose.
a brick red means glucose

The kidney

The kidney
The kidneys are organs that filter waste products out of the blood and excrete then e.g. urea along with water as urine.
Urea is made by the liver. Excess amino acids can’t be stored therefore the liver breaks them down to urea.(ornithine cycle)
OSMOREGULATION: The homeostatic mechanism of the active regulation of the osmotic pressure of bodily fluids to maintain the homeostasis of the body’s level of water, minerals and salts in the blood.
NITROGENOUS EXCRETION: excretion of nitrogen in urine.

The kidney is involved with the homeostatic functions of regulating the chemical properties of the blood. (Water, solvent concentration and pH)

When the blood passes through the kidney nephrons liquid is filtered out of the blood, carrying solutes with it, including urea. Useful nutrients are selectively reabsorbed and the wasted products are removed in urine.
There are two main stages of kidney function:

1) ULTRAFILTRATION
This occurs in the barrier between the blood and the filtrate in the Bowman’s capsule. In the Bowman’s capsule there is a dense network of capillaries called the glomerulus, blood flows into the capillaries.
A glomerulus is enclosed in the sac. Fluids from blood in the glomerulus are collected in the Bowman's capsule (i.e., glomerular filtrate) and further processed along the nephron to form urine. This process is known as ultrafiltration.
A high pressure caused by the blood moving into the capillaries via the afferent wide arteriole and moving out through the narrow efferent arteriole. The high pressure forces small molecules such as water, glucose, amino acids, sodium chloride and urea through the filter, from the blood in the glomerular capsule across the basement membrane of the Bowman's capsule and into the nephron. This type of high pressure filtration is ultrafiltration.
Blood is forced against the capillary endothelium which has pores in it which allow the blood plasma to reach the basement membrane and small molecules are squeezed about but large ones like protein and blood cells stay in.

2) Selective reabsorption (proximal tubule)
Selective reabsorption takes place in the proximal convoluted tubule (PCT) of the kidney. Blood leaving the Bowman’s capsule has a low hydrostatic pressure and so flows slowly. It has a high concentration as these could not pass out before. It therefore has a low water potential and this enables it to gain water from the proximal tubule. It is the process by which certain substances that are required by the body (such as glucose, amino acids, vitamins and water) but have been filtered out of the blood during ultrafiltration are reabsorbed. As only certain substances are reabsorbed, it is known as selective reabsorption.

substances secreted into the distal convoluted tubule are: h+ ions and potassium ions.
substances actively reabsorbed from the proximal convoluted tubule are sodium ions and glucose.
the kidney tubule has adaptation such as lots of mitochondria and a brush border for atp for the active reabsorption of molecules and a large surface area for absorption.
overview: sodium ions are actively pumped out, glucose reabsorbed, amino acids reabsorbed and chloride reabsorbed, 50 % urea reabsorbed

ADH makes the collecting duct more permeable to water. So more water is taken back into the body by osmosis. more water is taken back into the blood stream and less is lost in urine. It is secreted by the posterior pituitary gland. Osmoreceptors detect changes in the hypothalamus.

Urine: composition varies due to diet and climate.