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Responding to their environment helps organisms survive.

Our nervous system increases animals chances of survival as they respond to changes in their external environment, e.g. By avoiding spaces that are too warm or cold due to their living conditions.

Animals also respond to changes in their internal environment, making sure that their conditions are always right for their metabolism.

Plants also respond to changes in their environment to increase their chance of survival e.g. they sense the direction of light and grow towards it to maximise light absorption for photosynthesis.

These changes the organisms respond to in their internal or external environment are called STIMULUS.

The thing that detects the stimuli is called the receptor, the receptors in the sense organs (the eyes, ears, nose, tongue and skin) are groups of cells that detect external stimuli. E.g. rod and cone cells in the eye detect changes in light.

What responds to stimuli after its been detected by receptors is the Effectors, the effectors are cells found in glands e.g. the pancreas. Effectors respond in different ways - muscle cells contract, whereas glands secrete hormones.

The nervous system is made up of all the neurones (nerve cells) in your body. There are three types of neurone - Sensory neurones, Relay neurones and motor neurones.

The CENTRAL NERVOUS SYSTEM (CNS) consists of the brain and spinal cord only.

When the receptors in a sense organ detect a stimulus, they send electrical impulses along the sensory neurones to the CNS.

The CNS then sends these electrical impulses to an effector along a motor neurone. The effector then responds accordingly.

The job of the CNS is to coordinate the response. coordinated responses always need a stimulus, a receptor and an effector.

Because neurones transmit information using high speed electrical impulses, the nervous system is able to bring about very rapid responses.

Now as I've talked about how the nervous system and stimuli work to create a reaction according to the situation, I'm going to write about what happens after this reaction has occurred.

Even though your brain helps on how to quickly respond to a stimulus, sometimes it takes too long to make a decision on what to do, this is where Reflexes pop in.

Reflexes are automatic responses to certain stimuli - reflexes help reduce your chance of being injured.

For example, if someone shined a bright light in your eye, your pupils automatically get smaller so that less light gets into the eye, this helps the eye get damaged less.

Or if you get shocked the body releases the adrenaline hormone automatically so it doesn't wait for you to decide that you're shocked.

The route taken by the information in a reflex (from receptor to effector) is called a reflex arc.

The reflex arc goes through the central nervous system (CNS).

The neurones in reflex arcs go through the spinal cord or through an unconscious part of the brain.

When a stimulus (e.g. touching a hot object) is detected by receptors, an impulse is sent along a sensory neurone to the CNS.

In the CNS the sensory neurone passes on the message to another type of neurone, a relay neurone. The gap between two neurones is called a synapse. Messages are passed across synapses using chemicals.

Relay neurones relay the impulse to a motor neurone.

The impulse then travels along the motor neurone to the effector. (in this example its a muscle)

The muscle then contracts and moves your hand away from the stimulus.

Because you don't have to think about the response (which takes time) its quicker than normal responses.

Learning the relationship between DNA, Genes and Chromosomes.

In a cell contains a Nucleus - a Nucleus contains your genetic information/material in the form of Chromosomes.

Chromosomes are a long, continues strand of DNA, that has an x-shaped structure.

A gene is short section of DNA.

Human body cells are Diploid

Diploid means they have two copies of each chromosomes, arranged in pairs, a human cell nucleus contains 46 chromosomes in total - so the Diploid number for a human is 46.

DNA is a long list of instructions on how to put an organism together and make it work.

Each separate gene in a DNA molecule is a chemical instruction that codes for (says how to make) a particular protein.

Proteins are important because they control most processes in the body. They also determine inherited characteristics, e.g. eye colour, blood type.

By controlling the production of proteins, genes also control our inherited characteristics.

There can be different versions of the same gene, which give different versions of a characteristic - like blue or brown eyes. The different versions of the same gene are called alleles.

A DNA molecule has two strands coiled together to form the structure of a double helix (two spirals), the two strands are held together by chemicals called bases.

There are four different bases - adenine (A), cytosine (C), guanine (G) and thymine (T)

The bases are paired, and they always pair up in the same way - its always A-T and C-G. This is called complementary base-pairing.

Base-pairing means you'll always find equal amounts of A and T in a DNA sample - as well as equal amounts of G and C.

DNA is a type of nucleic acid, Nucleic acids are naturally occurring chemical compounds that serve as the primary information-carrying molecules in cells. They play an especially important role in directing protein synthesis.

As mentioned in my Photosynthesis post, Plants mostly reproduce asexually, however overall there are two ways an organism can reproduce (asexually and sexually) and also two ways a cell can divide (mitosis and meiosis) , although as seen in the title this post is going to explain Asexual reproduction and Mitosis.

Asexual reproduction involves Mitosis, an ordinary cell can make a new cell by simply dividing in two. Both new cells are genetically identical to the original cell - they both contain exactly the same genetic information, this cell division is known as Mitosis.

Some organisms produce offspring (children) using mitosis. This is known as asexual reproduction, Organisms which produce asexually include bacteria and some plants. (I will show some examples near the end).

Asexual reproduction involves only ONE parent. The offspring have identical genes to the parent - so there's no variation between parent and offspring, another word for asexual reproduction is cloning (I will do another post going more in depth about cloning).

Mitosis is when a cell reproduces itself by splitting to form two cells with identical sets of chromosomes.

Here's is how mitosis works:

In a cell that's not dividing, the DNA is all spread out in long strings, if the cell gets a signal to divide, it needs to duplicate its DNA - so there's one copy for each new cell. The DNA forms X-shaped chromosomes. Each 'arm' of the chromosome is and exact duplicate of the other.

The chromosomes then line up at the centre of the cell and cell fibres pull them apart. The two arms of each chromosome go to opposite ends of the cell.

Membranes form around each of the sets of chromosomes. These become the nuclei of the two new cells. (Nuclei is the plural version of nucleus)

Lastly, the cytoplasm divides. (The cytoplasm is the jelly-like substance inside a cell that holds organelles, supports cell shape, and allows chemical reactions to happen.)

You now have two new cells containing exactly the same DNA - they're genetically identical.

Mitosis also is how all plants and animals grow and repair damaged tissue.

Plants have several different ways of reproducing asexually, some plants do so by growing new plants from their stems.

An example of this is Strawberry Plants, The parent strawberry plant sends out runners - fast growing stems that grow out sideways, just above the ground.

The runners take root at various points (a short distance away) and new plants start to grow.

The new plants are clones of the parent strawberry plant, so there's no genetic variation between them.

This strawberry reproduction is an example of a natural method of asexual reproduction, but we can also clone them using artificial methods.

Gardeners can take cuttings from good parent plants, and then plant them to produce genetically identical copies (clones) of the parent plant.

Photosynthesis is the process of plants making 'food' (as it is ace), the 'food' that it is making is Glucose.

Photosynthesis happens within the green parts of plants, most commonly in leaves, this is because inside the plant cell there is something called Chloroplasts and inside of the Chloroplasts is a pigment that makes the plant green called Chlorophyll, which absorbs sunlight and uses this light energy to convert Carbon dioxide and Water into Glucose and Oxygen.

Photosynthesis is an important process as it transfers light energy into chemical energy (by energy transfer), which is stored in the Glucose. This chemical energy is released when broken down during respiration.

The word and symbol equations for photosynthesis is:

Carbon dioxide (6CO2) + Water (6H2O) -> Glucose (C6H12O6) + Oxygen (6O2) (The arrow is the process of sunlight being absorbed into the Chlorophyll)

Some extra information about photosynthesis:

Less sunlight/light energy would reduce the rate of photosynthesis being produced within the plant as Chlorophyll uses light energy to preform photosynthesis, so it can only do it as the light energy is arriving, so countries that have a a rainy/less sunny climate like: Colombia, Papua New Guinea, Panama etc... would experience less photosynthesis rather than countries with a sunny climate like: Mexico, Thailand, Australia etc... And also as obvious as it seems photosynthesis doesn't work when it its night time as the sun is hidden

To test a leaf for starch you would first need to remove the pigment (chlorophyll), how to do that is to add the leaf to boiling ethanol in a water bath that removes the pigment, after the pigment is removed the leaf should have a white colour, the reason we have this white colour is to see the presents of colour change, after we do this we wash the leaf with water to rehydrate and soften the leaf so then we spread it onto a white tile, and finally we add iodine from a dropping pipette onto the white leaf, iodine solution is used to test the presence of starch, the brown iodine should turn into a black/blue colour at the presence of starch.

When I mentioned that plants are 'ace', ace is short for asexual, plants can reproduce asexually, basically meaning they are single parents that generate genetic copies of themselves (I will do another post going in more depth of asexual reproduction)