Page 17 - Innovator's Science-8

Cells in all parts of a plant have tiny rod-shaped structures called plastids.
Some plastids, like chloroplasts, contain chlorophyll, which makes them

green and helps in photosynthesis. In non-green parts, they help in the
storage of substances. Plant cells also have a large, empty-looking space
called a vacuole. This helps the plant cell store important substances, get
rid of waste, and maintain the shape of the cell. This gives strength and

support to the plant. In animal cells, vacuoles are usually not present, if
present, they are usually small.
These small vacuoles store
certain substances dissolved in.

So, a cell is not just a simple bag of
liquid—it is a complex structure
made up of many different parts,
each with its own special function A schematic drawing of
to allow the cell, and in turn the (a) An animal cell and (b) A plant cell

entire organism to work.
We have now understood the basic structure of a cell. And we also

understand that plant and animal cells differ in their shape and structure. Do
different animal cells also vary in their shape and structure? Let us now see
how the shape and structure of different cells are related to the work they do.

VARIATION IN SHAPE AND STRUCTURE OF CELLS

Muscle cells and nerve cells have some similarities, but they also look quite
different. Both types of cells are designed to perform special jobs, so their
shapes help them work well. Muscle cells are shaped like spindles or thin
cylinders; they are designed this way to help them stretch and contract,

letting parts of the body move. Nerve cells are very long and thin, with
(a) Muscle cell branch-like endings that help send signals quickly across the body. Some
cells in our bodies are round, while others are long or have branches. Cells

look different from each other because each kind of cell performs a specific
job. The shape and structure of a cell match what the cell needs to do, so
the way a cell looks helps it do its job.
(b) Nerve cell
Cells come in different shapes and sizes because their unique forms help
Different cells in humans
them do specific jobs in the body. For example, inner cheek cells are thin
and flat to create a protective lining inside the mouth. Nerve cells, or
neurons, have long, branched shapes so they can send messages quickly

across the body. In plants, cells can be rectangular, tube-like, or elongated,
with some forming long tubes to carry water. In the human digestive
system, muscles cells in the food pipe contract and relax to push food

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Science-8