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What you need to know
Reflections and Exam tips
Different parts of the body need to communicate with each other for things to work well, this is called co-ordination. Animals evolved 2 mechanisms of co-ordination, mainly for survival. These are:
The Central Nervous system
Our nervous system is made up of Nerve Cells, also called Neurons. These are cells that are specialised to carry messages over long distances, so they are long, more like a wired/landline phone (we say elongated in proper Biology speak).
All over the body, we have receptors which detect incoming messages (stimuli). These are groups of sensitive cells which are located in sense organs:
Structure of main types of nerve cells
Nerve cells are just like any other animal cell except that they have a few adaptations that enable them to detect and carry messages around the body.
There are 3 main types of neurons:
The effector is part of the body that brings about the required change. It can be a muscle or a gland.
Glands are a tissue which is specialised to make and secrete a particular chemical or hormone.
Neurons are not joined up together. There are small gaps between one neuron and the next, more like switches.
The gaps between neurons are called Synapses. When an impulse reaches the synapse, a conducting chemical called a neurotransmitter is released. This allows the impulse to pass through the gap. After the impulse has passes, the neurotransmitter is broken down and reabsorbed.
Unfortunately, because the neurotransmitter has to diffuse across the gap/synapse, it results in a small delay of about 0.2 milliseconds. Not much, is it? Since there are many more synapses along the route of the impulse, the delay accumulates and becomes substantial.
The Reflex pathway
A Reflex is a quick, automatic response to a stimulus. It does not need you to think, you just do it. Ever said 'that was a knee-jerk reaction'?
Why do we need reflexes?
If we had to think about the response, it would take too long to react and damage our affected body part or even get us killed!!! This is because of many synapses that the impulse will need to cross causing a significant delay.
Reflex arc/pathway- is the order of neurons that the impulse follows during a reflex action. In simple terms, this is:
Receptor- Sensory Neuron- Relay Neuron- Motor Neuron- Effector
Just memorise this and you will be ok for exams....
Co-ordination is also about keeping body conditions the same and confortable to support life processes. This is called Homeostasis. Our bodies need to keep these constant to sustain a healthy life:
The Menstrual cycle
The menstrual cycle is the series of changes that take place in the female reproductive cycle over 28 days. There are at least 4 different hormones that are responsible, these and the major events are summarised below.
Changes in the uterus lining
Hormones and their roles
Controlling fertility- The pill, fertility drugs and IVF
1. The pill
The contraceptive pill was developed by Gregory Pincus in the 1950s. Pincus carried out a controverisal test of the pill on Puerto Rican women in the ealy 1950s. It is widely held responsible of the 1960s 'swing' where women felt sexually liberated to have sex without fear of getting pregnant.
The most common type of pill is the Combined pill containing both Oestrogen and Progesterone. Oestrogen inhibits FSH production which means no eggs mature = no pregnancy. Progesterone thickens mucus at the cervix so that sperm may not penetrate through to the uterus.
IVF stands for In Vitro Fertilisation. (vitreous- glass)- Literally meaning fertilisation in a glass container (petri dish).
IVF is used to help women who cannot conceive naturally. The steps are:
IVF pros and Cons
Plant Hormones- Tropisms
Plants also show various responses. They respond to water, sunlight and gravity. These growth responses are called Tropisms and are controlled by a growth hormone called Auxin.
Auxin is produced at the tips of shoots and roots.
Auxin diffuses to the shaded part of the shoot and stimulates cell growth. So the region in darkness grows longer than the one receiving light and the shoot bends towards light. This is called phototropism.
Auxin is attracted down by gravity where it slows down cell growth. The part above therefore grows more cells, causing the root to bend downwards. This is called geotropism or gravitropism.
Shoots are negatively geotropic (grow away from gravity) and positively phototropic (grow towards light).
Roots are positively geotropic and negatively phototropic.