Biology : B5

Define homeostasis.

Maintaining a stable internal environment.

How does homeostasis occur?

A receptor detects a stimulus which is sent to a co-ordination centre to co-ordinate a response, which is carried out by the effector.

What are the 2 control systems?

1. Nervous system

2. Hormonal system

What are negative feedback loops?

When a level is too low or high, a negative feedback loop brings it back to normal using control systems.

What are the 2 types of receptors?

Muscles and glands.

How is temperature kept constant?

Keep warm = shivering, goosebumps, vasoconstriction.

Keep cool = sweating, vasodilation

Define reaction time

The length of time taken to respond to a stimulus.

How do we measure reaction time? (Practical)

1. The person being tested should sit and rest their arm at the table edge.

2. A second person will hold a ruler vertically - the zero being level with their thumb.

3. Drop the ruler without warning and record the number they catch it (the bigger the number = the slower the reaction time)

4. Repeat several times and calculate a mean.

To see the effect of caffeine:

1. Take a caffeinated drink and wait 10 minutes.

2. Carry out the experiment again ands record a mean.

3. Compare values from a table.

What is the nervous system made up of?

Brain, spinal chord and nerve cells (neurones).

What is the CNS?

Consists of brain and spinal chord - a coordination centre.

What are the 3 neurones and parts that make up a response?

1. Sensory neurones = caries signals from effectors to CNS

2. Motor neurones = carries signals away from CNS to receptor

3. CNS = receives information and sends impulse to effectors

How is a nervous system response carried out?

STIMULI (detected by) RECEPTOR (sends impulse to) SENSORY NEURONE (which carries impulse to) CNS (carries signal through to) EFFECTOR (formulates a) RESPONSE.

Define hormones.

Chemical messengers that travel through the blood.

What is the difference between a hormonal response and a nervous response?

Hormonal responses are slower but longer lasting.

What is the endocrine system?

The collection of glands that produce hormones to regulate metabolism, growth and development, tissue function, sexual function, reproduction and sleep.

What are the 6 glands within the endocrine system? What hormones do they produce and what do they do?

1. Pituarity gland = many hormones = master gland

2. Thyroid = thyroxine = regulates metabolism and growth

3. Pancreas = insulin and glucagon = regulates blood sugar

4. Adrenal gland = adrenaline = prepare for fight/flight

5. Ovaries (Female) = oestrogen and proestrogen = menstrual cycle

6. Testes (Male) = testosterone = controls puberty and sperm production

Define a reflex.

Rapid, automatic responses to certain stimuli that don not involve the conscious part of the brain.

How is a reflex arc carried out?

STIMULI (detected by) RECEPTOR (sends impulse to) SENSORY NEURONE (to the) CNS/spinal chord (sends signal through) RELAY NEURONE (passes signal to) MOTOR NEURONE (to the) EFFECTOR (formulates a) REPONSE

What is a synapse?

The synaptic cleft/gap between two neurones where they connect.

How does a signal cross the synapse?

• The signal is sent electrically through the first neurone

• To the pre-synaptic neurone at a synaptic cleft

• Synaptic cleft is the gap between two neurones

• The signal changes from electric to chemical and diffuses through the neuro-transmitters

• Once it passes through it converts back to an electrical impulse and continues along the second neurone as an electrical signal

How are neurones adapted?

Myelin sheath = transport electrical impulses

Branched connections = pass signal through the whole body

Long = quickly carry the signal

How is adrenaline used in ‘fight or flight’?

Prepares the body for a life-threatening situation.

Give examples of the effect of adrenaline.

• Dialating pupils

• Increased blood glucose

• Increased heart and breathing rate

• Increased oxygen supply

• Muscles tense

• Increased supply of blood and glucose to muscles

Define metabolism.

The rate at which all chemical reactions within the body happen.

What does thyroxine do?

Regulates metabolism and is important in growth and development.

How does iodine correlate top thyroxine?

Iodine is needed for thyroxine production.

A lack of iodine means there is not enough thyroxine to inhibit the production of TSH.

How does thyroxine work as a negative feedback loop?

Blood thyroxine level high —> Pituitary gland inhibits TSH production in thyroid —> Normal levels return

Blood thyroxine level low —> Pituitary gland stimulates TSH production in thyroid —> Normal levels return

Comprare a hormonal and versus response.

Nervous = very fast, short time, precise area

Hormonal = slower, long time, general area

What happens when blood sugar is too high?

It’s detected by the pancreas which produces insulin by changing glucose to glycogen causing glucose to move into the muscles and liver (stored as glycogen) for later use. Glucagon production is inhibited.

What happens when blood glucose is low?

It’s detected by the pancreas which produces glucagon by changing glycogen to glucose that’s was stored in the liver or muscles to increase blood glucose. Insulin is inhibited.

What is diabetes?

The inability to control blood sugar.

What is type 1 diabetes?

When the pancreas produces too little or no insulin, it is from birth and hereditary. Treated by insulin injections.

What is type 2 diabetes?

When the body becomes resistant to insulin, caused by an unhealthy lifestyle, treated through lifestyle changes e.g. diet and exercise.

What are the 4 hormones involved in menstruation? Where are they made and what do they do?

FSH = Pituarity glands = matures the eggs

Oestrogen = Ovaries = Inhibits FSH production and thickens uterus lining. Stimulates LH production.

LH = Pituarity glands = causes ovulation.

Proestrogen = Ovaries = Maintains uterus lining. Inhibits LH.

What are the 4 stages of the menstrual cycle and what days do they occur?

1. Uterus lining sheds (DAY 1-4)

2. Uterus lining grows back (DAY 4-14)

3. Eggs are released (DAY 14)

4. Uterus lining maintained (DAY 14-28)

Define fertility

How easy it is for a woman to get pregnant.

Define contraception

Things that prevent pregnancy.

How does IVF work?

• FSH is given to stimulate the production of multiple eggs maturing

• LH is given to cause ovulation

• Fathers sperm is added to a petri-dish

• Embryos are screened for genetic diseases

• 1 or 2 embryos are implanted into the womb

What are the advantages and disadvantages of IVF?

AVD =

• Infertile couples can have children

• Removes genetic diseases

DIS =

• Expensive

• Low success rate

• Ethical issues regarding embryo discard

• “Designer babies”

• Multiple births can put mother at risk

Why are oestrogen and proestrogen used within hormonal contraceptives?

They inhibit the production of LH and FSH which cause the egg to mature and ovulate.

What are the 5 hormonal contraceptives and how do they work?

1. The oral pill = taken everyday ands releases proestorgen and oestrogen, has side effects and is 99% effective.

2. Contraceptive patch = releases proestrogen and oestrogen directly into the bloodstream for a week.

3. Contraceptive implant = stimulates and releases proestrogen and oestrogen for up to 3 years in the arm.

4. Contraceptive injection = stimulates and releases proestrogen and proestrogen into the bloodstream for up to 3 months.

5. IUD (copper) = placed in uterus to kill sperm. IUD (plastic) = placed in uterus and releases hormones to prevent ovulation.

What are the 5 barrier contraceptives and how do they work?

1. Condoms = trap sperm and prevent STD’s

2. Diaphragm - blocks sperm entering the cervix

3. Spermicide = gel substance that kills sperm

4. Abstaining = not having sex

5. Surgery = removal of fallopian tubes or sperm duct