PLANTS

Plants are living organisms belonging to the kingdom Plantae.
They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae.
The scientific study of plants, known as botany

Green plants absorb light energy using chlorophyll in their leaves.
They use it to react carbon dioxide with water to make a sugar called glucose.
The glucose is used in respiration, or converted into starch and stored.
Oxygen is produced as a by-product.
This process is called photosynthesis.
Temperature, carbon dioxide concentration and light intensity are factors that can limit the rate of photosynthesis.
Plants also need mineral ions, including nitrate and magnesium, for healthy growth. They suffer from poor growth in conditions where mineral ions are deficient.

Photosynthesis

Photosynthesis is the chemical change which happens in the leaves of green plants.
It is the first step towards making food - not just for plants but ultimately every animal on the planet.
During this reaction, carbon dioxide and water are converted into glucose and oxygen.
The reaction requires light energy, which is absorbed by a green substance called chlorophyll.
Photosynthesis takes place in leaf cells. These contain chloroplasts, which are tiny objects containing chlorophyll.

Here is the equation for photosynthesis:

 Plants absorb water through their roots, and carbon dioxide through their leaves. Some glucose is used for respiration, while some is converted into insoluble starch for storage. The stored starch can later be turned back into glucose and used in respiration. Oxygen is released as a by-product of photosynthesis.

Factors limiting photosynthesis

1. Light intensity
2. Carbon dioxide concentration and 
3. Temperature.

• Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis. 
• Photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide.
• If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot.
  
  

  Maximising growth

  Farmers can use their knowledge of these limiting factors to increase crop growth in greenhouses. They may use artificial light so that photosynthesis can continue beyond daylight hours, or in a higher-than-normal light intensity. The use of paraffin lamps inside a greenhouse increases the rate of photosynthesis because the burning paraffin produces carbon dioxide, and heat too.
  
  

  Plants and minerals

  Plants need to take in a number of elements to stay alive. The most important are:
• carbon
• hydrogen
• oxygen

Plants get hydrogen and oxygen from water in the soil, and carbon and oxygen from carbon dioxide and oxygen in the atmosphere. Water and carbon dioxide are used to synthesise food during photosynthesis. Oxygen is used to release energy from food during respiration.
In addition to these three elements, plants need a number of minerals for healthy growth. These are absorbed through the roots as mineral ions dissolved in the soil water. Two important mineral ions needed by plants are:

• nitrate - for making amino acids, which are needed to make proteins
• magnesium - for making chlorophyll

If a plant does not get enough minerals, its growth will be poor. It will suffer from deficiency symptoms:

• deficient in nitrate - it will suffer from stunted growth
• deficient in magnesium - it's leaves will turn yellow

The tomato plant on the left is healthy, the one on the right is growing in conditions where mineral ions are deficient


SOURCE

1. http://en.wikipedia.org/wiki/Plant
2. http://www.bbc.co.uk/schools/gcsebitesize/scien/add_aqa/plants/plants1.shtml

Mixtures & Compounds

A mixture occurs when you combine matter in such a way where the components can be separated again.

 A compound results from a chemical reaction between components, forming a new substance.

For example, you can combine iron filings with sulfur to make a mixture. 

All it takes is a magnet to separate the iron from the sulfur.

 

On the other hand, if you heat the  iron and sulfur you form iron sulfide which is a compound.

Here is How 

First form a mixture - Stir some iron filings and sulfur to form a powder. You have just taken two elements and combined them to form a mixture. You can separate the components of the mixture by stirring the powder with a magnet  - iron will stick to the magnet -

If you heat the mixture over a Bunsen burner, hot plate or stove, the mixture will start to glow. The elements will react chemically to form iron sulfide which is a compound. Careful! Unlike the mixture, the formation of a compounds cannot be undone so easily

 What you Need

• iron filings 
• sulfur powder
• magnet
• test tube or beaker
• Bunsen burner or hot plate or stove

 A compound is a material that is made up two or more elements chemically joined together.
For example , water is a compound made up of the elements hydrogen  (H) and oxygen (O). 


A compound such as water has particles called molecules.

Water

• We can represent a water molecule by writing a chemical formula: H2O.

• This tells us that a molecule of water contains two atoms of hydrogen joined to one atom of oxygen.
• Water is made up of many identical water molecules. 
• Water is a liquid, so the molecules are close together.

Carbon dioxide

•  Chemical formula: CO2.
•  one carbon atom joined to two oxygen atoms make a molecule of  carbon dioxide
• Carbon dioxide is a gas, so the molecules are further apart than in water

Sodium chloride (common salt)

• Formula - NaCl
• There is one sodium particle for every chlorine particle
• NaCl is a solid, the sodium and chlorine particles in it are close together with strong forces between them

The cards below show information about some materials. Some of them are elements and some are compounds.

Signs of a chemical reaction

ATOMS AND ELEMENTS

 Before starting this unit, you should already be familiar with these ideas from earlier work.

• Matter is all the material in the Universe. Everything  we know rocks, air,water, plants, animals andeven humans is made of matter. Matter can  exst in three states as a solid, as a liquid and a gas.
   
• If we cannot see and touch something in science, we can use a model to help show us how it works. What model have you used to represent circuits?

• The particle model suggests that all matter is made up of particles. How are the particles arranged in a solids, liquids and gases?
• Matter sometimes changes state from solid to liquid or liquid to gas and back again. Boiling is one change of state. List some others.
• All matter is made up of  tiny particles called atoms.
  material that is made of only one type of atom is called an element.
  
  
   Elements are found naturally on Earth and in space although some have been created in laboratories in recent times. 
• The elements were not all discovered at once, and some are very recent discoveries.
   

ATOMS

All matter is composed of atoms.

Atoms are the smallest pieces of a substance that can exist.

Atoms are very, very tiny. You cannot see atoms, not even with a microscope.

Scientist have done many experiments to find out about atoms.

They use the results of their experiments to develop theories or models to help us understand what atoms are like and how the behave.

At the centre of the atom there is a core called the nucleus .

The nucleus is made up of sub-atomic atoms (smaller than atoms)  called protons and neutrons.

All around the core is an area of spinning electrons.

They remain in place because  they are attracted to the opposite charge of the protons and the neutrons.

The protons have a positive charge and neutrons have no electric charge

Hydrogen atoms are the only atoms without neutrons

A normal atom has the same number of protons as electrons.

The atomic number of an atom tell you how many proton it has.

         Atomic             Number of          Number of

        Number     =     Protons      =      Electrons

 

Electrons are much smaller than protons, they weigh almost nothiing.

The atomic mass of an atom depends on the number of protons and neutrons in the nucleus

Carbon has an atomic mass of twelve.

The number of protons and neutrons is called the mass number of atoms.

Mass Number (A)   =   Atomic          +        Number of

                                      Number(z)              Neutrons