Trees are tall plants with hard and thick stems (trunks). The main trunks of large trees like the mango and the banyan bear many branches, which further divide into smaller branches. Leaves grow on these branches. Branching causes the tree to spread out wide on all sides. Trees are Nature's wonders and a great gift to mankind as well as to all those who depend on them. While some dependants stay on the trees, others come to them to rest or to feed. Still others use them to raise their offspring. Humans have used almost any and every tree to their benefit. It is very sad that the same humans are destroying trees all over the world in the name of "development". This can be to create factories, new townships, wider roads, railways, entertainment centres and so on. They do not realise that they are making a big mistake.Trees are useful to us in many ways. 1. Food: Trees give us food such as fruits. These provide us with excellent nourishment. 2. Wood: The wood from some trees such as teak, walnut, rosewood and oak is used to make furniture. Wood from other trees is used as fuel for cooking and for warming houses. 3. Paper: Paper is made from wood. 4. Medicines: Many trees are the source of useful modern medicines. 5. Shelter: The canopy of leaves and branches gives us shelter. 6. Climate: Trees provide cool shade. Many trees, for example, in a forest, can make the climate pleasant and the air clean. 7. Rain: Forested areas get better rainfall compared to areas with no tree cover. 8. Oxygen: When trees respire, they release oxygen that all animals need for their survival.Examples of usefulness of trees: Have you eaten an apple? A mango? Then you will know what I mean when I say that trees provide food. Other fruits like jackfruit, coconut and figs also grow on trees. Most of the furniture in any house is made from wood. In mountainous regions, even the walls are made from logs of trees. In cold areas, where people need to heat their homes, wood from trees is used for heating. Many medicines are derived from trees. These include medicines for fever, malaria and heart-diseases. By absorbing the extra carbon dioxide and releasing oxygen, trees help make the environment clean and more suitable to live in. Forested areas are pleasantly cool, get better rainfall and have cleaner air. Many trees are grown especially for their products, such as the rubber tree, which gives us rubber that is so useful to us. Nowadays, a lot of rubber is made synthetically in factories.
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I'm giving o global warming Hope this helps....

Good morning to my respected teachers and my dear friends, I would like to speech on the topic of global warming today. Global warming is mainly caused by the increasing concentration of greenhouse gases in the earth’s atmosphere. Some of the greenhouse gases are CO2, water vapour, methane, nitrous oxide and ozone. When these gases get collected to the lower environment, it makes a cover which easily allows all the hot radiations of sun to the earth however restrict its escape back to the space. This process is called as the Green House Effect. Such gases in the atmosphere trap hot radiations and keep earth warm by increasing temperature.

The level of green house gases also raise because of the human activities such as burning trees, burning fissile fuels, electric lights, use of refrigerator, microwave, air conditioner, and other electric machines. Such process releases high percentage of carbon dioxide and other green house gases into the atmosphere causing the earth temperature to rise. Rise in heat causes more water from earth to evaporate into atmosphere, water vapor again absorbs more heat and makes earth atmosphere warmer. Global warming has changed natural processes rainfall patterns, length of seasons, rise of sea level, ecology balance and many more. It is a powerful demon affecting our lives to a great extent so it needs to be solved on urgent basis by the effort of all of us.

Thank You