discovering cells part 2 - quia · 1 discovering cells -part 2. 10/19/18 2 parts of a cell wcells...
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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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