Discovering Cells Part 2 - Quia · 1 Discovering Cells -Part 2. 10/19/18 2 Parts of a Cell wCells come in many shapesand sizes, and may be specialized for different functions. But

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Discovering Cells - Part 2

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Parts of a Cell

w Cells come in many shapes and sizes, and may be specialized for different functions. But all cells have some parts in common.

w All cells have a cell membrane. w The cell membrane is a protective layer

that covers the cell�s surface and acts a barrier.

Parts of a Cell, continuedwThe cell membrane separates the

cell�s contents from its surroundings.

wThe cell membrane also controlsthe materials going into and out of the cell.

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Cell Membrane

Parts of a Cell, continuedw Most of the contents of a

cell, including the fluid, is called the cytoplasm.

w Organelles are part of the cytoplasm.

w Organelles are structures that have specific jobs inside the cell.

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Parts of a Cell, continuedw All cells have DNA (deoxyribonucleic acid) at some

point in their lives. w DNA is the genetic material that carries instructions for

making new cells.

w In eukaryotic cells, including plants and animals, the DNA is found within the nucleus of the cell.

w The nucleus is an organelle specialized to hold the DNA.

w The nucleus plays a role in growth, metabolism, and reproduction.

Parts of a Cell, continuedw Bacteria have DNA, but do not have a nucleus.

w Their DNA floats free in the cytoplasm.

w Human blood cells have a nucleus and DNA as they are growing. Once mature, they lose their DNA and nucleus.

w Most cells, however, need DNA throughout their lives. The DNA provides instructions for making proteins.

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The Nucleus

Two Kinds of Cells

Sect 4-1

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Two Kinds of Cellsw Cells that do not have a nucleus are called prokaryotes. w Bacteria and archaea are prokaryotes.

w Prokaryotic DNA is a round molecule, twisted like a rubber band.

w Prokaryotes have cell walls. They lack the membrane-bound organelles found in other organisms.

Two Kinds of Cells, continuedw Eukaryotes are organisms made up of cells that

have a nucleus enclosed by a membrane.

w Eukaryotic cells are 10 times as large as prokaryotic cells, although most eukaryotic cells are still microscopic.

w Eukaryotes have membrane-bound organelles to carry out the functions of the cell.

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