Download Key Idea #11

Key Idea #11

Cells in multicellular organisms are
specialized to take in nutrients, which
are used to make the materials that a
cell or organism needs.
Nutrients taken in by the cell
provide materials to build
cell structures (organelles) and
 specialized molecules used by the
organisms:

– carbohydrates
– lipids (fats)
– proteins
– nucleic acids: DNA and RNA
Organic and Inorganic Compounds


Organic Compounds
– contain carbon
• include carbohydrates, proteins, lipids, and
nucleic acids
Inorganic Compounds
– do not contain carbon*
• includes water, sodium chloride (table salt) and
carbon dioxide* - an exception
Carbon dioxide and water are used to produce
carbohydrates, proteins and fats (lipids).
http://library.thinkquest.org/C004535/media/cell_membrane.gif
Carbohydrates


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are energy-rich compounds made of the elements
carbon, hydrogen, and oxygen
are an important part of cell membranes and cell
walls
include sugars
– fruits and some vegetables

include starches
– potatoes, noodles, rice, and bread contain starch that your
body breaks down into glucose (a sugar)
Proteins





are large organic molecules make of carbon,
hydrogen, oxygen, nitrogen and sulfur.
are found in foods such as meats, eggs, fish, nuts
and beans
form parts of cell membranes
make up many of the organelles found in cell
are used by cells in your body to build body parts
such as hair.
Lipids



are energy-rich compounds made of carbon,
hydrogen, and oxygen.
include fats, oils, and waxes.
includes cholesterol
– an important part of animal cell membranes
– Meat, cheese, and eggs are all high in cholesterol
Nucleic Acids


are very large organic molecules made of carbon,
oxygen, hydrogen, nitrogen, and phosphorus.
contain the instructions needed to carry out life.
– DNA
• genetic material that contains the information that is
passed from parent to offspring
– RNA
• important for protein production
• found in the cytoplasm and nucleus
Water
must be present for most chemical
reactions to take place.
 helps cells keep their size and shape

Diffusion and Osmosis
Cell Membrane
acts as a gatekeeper
 is selectively permeable

– controls what substances can enter or
leave the cell
is permeable to oxygen, water, and
carbon dioxide to pass through it
 is not permeable to some large
molecules and salts

Substances that can move into
and out of a cell use one of three
methods:
Diffusion
 Osmosis
 Active Transport

Diffusion – Molecules in Motion

Diffusion is the main method by which small
molecules move from an area of higher
concentration to an area of lower
concentration.

http://www.mrphome.net/physics/diffusion/index.html
What causes diffusion?

Molecules bump into each other and
eventually spread out evenly throughout
an area.
– Example: Air freshener spreads out when
you spray it.
When there is a higher concentration of
molecules outside a cell than inside a cell


the molecules diffuse (move) into the cell until there is
an equal number of molecules inside and outside the
cell.
These molecules can be oxygen, carbon dioxide or
water
http://www.indiana.edu/~phys215/lecture/lecnotes/lecgraphics/diffusion.gif
When the molecules are equal on both sides of
the cell membrane, it is called equilibrium.
Googleimages.com
Osmosis

is a type of diffusion.

is the diffusion of
water molecules
through a selectively
permeable membrane.

is important to cells
because they can’t
function properly
without adequate
water.
Note: Only water molecules
pass through the membrane
during osmosis
http://www.biologycorner.com/resources/osmosis.gif

occurs when water
molecules move from
an area of higher water
concentration to an
area of lower water
concentration until
equilibrium is reached.

Note: other dissolved
particles can’t pass
through the membrane
FYI:
A simple rule to remember is:
When salt is concentrated inside or outside the cell
membrane, it will draw the water in its direction.
This is why
•you get thirsty after eating something salty because the excess
salt draws water to the cells in the body.
•people lost at sea will speed up dehydration (and their death) by
drinking sea water.
•“salting fields" was a common tactic used during wars to cause
food shortages.
http://www.biologycorner.com/bio1/diffusion.html
Osmosis & different concentrations of solute:
In normal cells:

the amount of
dissolved salt
molecules is equal on
both sides of the cell
membrane.
 the water moves back
and forth but the
overall amount of
water on either side
remains the same.
http://www.biologycorner.com/bio1/diffusion.html
When there are more dissolved salt
molecules inside the cell than outside the
cell:

water moves into
the cell since “salt
sucks”.

the cell grows
larger.
http://www.biologycorner.com/bio1/diffusion.html
In plant cells this causes

the central
vacuoles to fill with
water and the
plant becomes
rigid.

Note: The cell wall
keeps the plant
from bursting.
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/aplantturgor.gif
In animal cells

the cells may be in
danger of bursting.

contractile vacuoles
pump water out of
the cell to prevent
this.
Googleimages.com
When there are more salt molecules
outside the cell than inside the cell

the water is sucked
outside the cell.

the cell shrinks.
http://www.biologycorner.com/bio1/diffusion.html

In plant cells, the central vacuole loses
water and the cells shrink, causing wilting.
 In animal cells, the cells also shrink and
shrivel up.
 In both cases, the cell may die.
FYI: Why can’t fish live in both fresh and salt
water?
Salt water fish
have cells that don’t
contain as much salt
as the salt water they
live in
 cells lose a lot of
water into the water
around them by
osmosis
 must drink a lot of
water and produce
little urine to
compensate

Fresh water fish

have cells that contain
more salt than the fresh
water they live in
 cells gain water from
their surroundings by
osmosis
 don’t usually drink water
and produce large
amounts of urine to
compensate
Substances move in and out of cells by

passive transport
– no energy is needed
• diffusion
• osmosis

active transport
– cell uses energy (ATP)
• engulfing
• contraction of vacuole wall eliminates waste
• transport proteins in the cell membrane pick up
molecules outside the cell and carry them in
http://www.dwm.ks.edu.tw/bio/activelearner/05/images/ch05summary.jpg
Nutrients that can’t pass through the cell
membrane by diffusion can be taken
into the cell through active transport.
 Active transport uses the cells energy to
accomplish this.

Active Transport
Active transport examples:
 engulfing

transport proteins in the cell membrane pick up
molecules outside the cell and carry them in
http://www.nicksnowden.net/images/Membranes_and_Transport/endocytosis.gif ; phschool.com.jpg