Download Describing Matter & Energy

The Cell in its Environment
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The cell membrane acts as a gatekeeper  it’s
selectively permeable, meaning it controls what
enters and leaves a cell
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Diffusion is the process by which molecules tend to
move from an area of higher concentration to an
area of lower concentration (similar to weather &
high/low pressure areas)
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Osmosis is the diffusion of water molecules through
a selectively permeable membrane
The Cell in its Environment
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The movement of material through a cell
membrane without using energy is called passive
transport
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The movement of material through a cell when
energy is used is called active transport.
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Diffusion and osmosis are 2 examples of passive
transport
Transport protiens and engulfing are 2 examples of active
transport.
Small cell size is an advantage because substances
can travel faster through the cytoplasm of small
cells
The Cell and Energy
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During photosynthesis, cells capture energy from
sunlight and use it to change carbon dioxide gas
and water (raw materials) into oxygen and sugars,
such as glucose (products)
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6C02 + 6H20  C6H12O6 + 6O2
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During respiration, cells break down simple food
molecules such as glucose and release the energy
they contain.
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Photosynthesis and respiration can be thought of as
opposite processes
The Cell and Energy
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Fermentation is an energy releasing process that
does not require oxygen
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This is necessary for the survival of some single-celled
organisms that may live wehre there is no oxygen, for
example in the mud of lakes or swamps
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Alcoholic fermentation occurs in yeast and some other
single-celled organisms
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Lactic acid fermentation occurs, for example, when an
athlete’s muscles run out of oxygen
Cell Division
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To divide into 2 equal parts, a cell would need to
either duplicate the structures (organelles) or divide
them equally between the two new cells
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The regular sequence of growth and division that
cells undergo is known as the cell cycle
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There are 3 main stages of the cell cycle – one
“parent” cell divides to form two identical
“daughter” cells
Cell Division
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Stage 1: Interphase:
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The period before cell division occurs
The cell grows to its mature size, makes a copy of its
DNA (DNA replication) and prepares to divide into 2 cells
At the end of interphase, the cell is ready to divide
Stage 2: Mitosis:
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The stage during which the nucleus divides into 2 nuclei
One copy of the DNA is distributed into each of the 2
daughter cells
Mitosis is divided into 4 parts - Prophase, Metaphase,
Anaphase, Telophase
Cell Division
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Prophase – chromatin in the nucleus begins to
condense and coil. Because of DNA replication,
each rod has doubled and is now called a
chromosome.
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As the cell progresses through metaphase,
anaphase and telophase, the chromatids separate
from each other and move to opposite ends of the
cell.
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At this point, 2 nuclei form around the chromatids
at the 2 ends of the cell. This completes mitosis.
Cell Division
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Stage 3: Cytokinesis:
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This is the final stage of cell divison – usually starts
around the same time telophase does.
The cytoplasm divides and distributes the organelles in
each of the 2 new cells
This stage differs between plant and animal cells because
of the cell membrane versus the cell wall – Why would
this cause a difference?
At the end of the cell cycle, each daughter cell has the
same number of chromosomes as the original parent.
The length of the cell cycle differs between cells
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Some cells such as human brain cells do not divide, and
remain in interphase for as long as they live.
Cell Division
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DNA Replication
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This ensures that every daughter cell will have all of the
genetic information it needs to carry out its activities
A DNA molecule is often described as a double helix
The sides are made up of sugar (deoxyribose) and
phosphate molecules
The rungs are formed by pairs of 4 nitrogen bases
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Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)