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www.GOALias.blogspot.comCellsYou have seen that buildings are made of bricks.Similarly, the bodies of living organisms aremade of tiny units called cells. Cells can be seenonly under the microscope. Some organismsare made of only one cell. The cell is enclosed bya thin outer boundary, called the cell membrane.Most cells have a distinct, centrally locatedspherical structure called the nucleus (Fig. 1.1).The nucleus is surrounded by a jelly-likesubstance called cytoplasm.NucleusCytoplasmCell membraneFig. 1.1 Cellleaves. Carbon dioxide from air is takenin through the tiny pores present on thesurface of the leaves. These pores aresurrounded by ‘guard cells’. Such poresare called stomata [Fig. 1.2 (c)].Boojho wants to know how waterand minerals absorbed by rootsreach the leaves.Water and minerals are transportedto the leaves by the vessels which runlike pipes throughout the root, the stem,the branches and the leaves. They forma continuous path or passage for thenutrients to reach the leaf. You will learnabout transport of materials in plantsin Chapter 11.Paheli wants to know what is sospecial about the leaves that theycan synthesise food but otherparts of the plant cannot.The leaves have a green pigmentcalled chlorophyll. It helps leaves tocapture the energy of the sunlight. Thisenergy is used to synthesise (prepare)food from carbon dioxide and water.Since the synthesis of food occurs in thepresence of sunlight, it is calledphotosynthesis (Photo: light; synthesis :to combine). So we find that chlorophyll,sunlight, carbon dioxide and water arenecessary to carry out the process ofphotosynthesis. It is a unique processon the earth. The solar energy iscaptured by the leaves and stored in theplant in the form of food. Thus, sun isthe ultimate source of energy for allliving organisms.Can you imagine the earth in theabsence of photosynthesis!In the absence of photosynthesisthere would not be any plants. Thesurvival of almost all living organismsdirectly or indirectly depends upon thefood made by the plants. Besides,oxygen which is essential for the survival2SCIENCE