Cell Function
7-3 Cell Boundaries

A cells survival depends on its ability to maintain homeostasis and get nutrients
 Homeostasis – dissolved substances are equal inside and outside the cell
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Cell Membrane
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Regulates what enters and leaves the cell
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Selective Permeability
– the cell membrane allows some molecules into the cell while keeping others out
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Made of a phospholipid bilayer – two layers of phospholipids
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Phospholipid
– lipids with a phosphate head and fatty acid tails
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The two fatty acid tails repel water and the phosphate heads don’t
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Water soluble molecules will not easily move through the membrane because they are stopped by the fatty acid tails
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Fluid Mosaic Model
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Fluid because the membrane is flexible
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Mosaic because proteins, carbohydrates, lipids, embedded in it
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Transport Proteins
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Span the entire membrane
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Allow needed substances or waste materials to move through plasma membrane
1

Passive Transport
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Passive transport – no energy is required to move particles across membranes by diffusion
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3 Types of Passive Transport
1. Diffusion
2. Osmosis
3. Facilitated Diffusion
Diffusion
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Diffusion – net movement of particles from an area of high to low concentration
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Diffusion is a slow process because it relies on the random motion of molecules
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Dynamic Equilibrium
– concentration of solutes is equal inside and outside the cell
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Concentration Gradient
– difference in concentration of a substance across space
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Because molecules diffuse from an area of high to low concentration, they move with the gradient, and does not require the cell to use energy
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Diffusion will continue until there is no concentration gradient
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3 Factors That Affect Diffusion
1. Concentration
– the more concentrated the substance the more rapidly diffusion occurs
2. Temperature – increase temperature increase diffusion
3. Pressure
– increase pressure increase diffusion
Osmosis
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Osmosis – the diffusion of water across a selectively permeable membrane from an area of high to low concentration
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water flows to the side of the membrane where the water concentration is lower
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3 Types of Solutions Cells Can Be In
1. Isotonic Solution
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The concentration of dissolved substances is equal inside and outside the cell
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Most solutions injected into the body are isotonic, so that cells are not damaged by the loss or gain of water
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The concentration of dissolved substances is in equilibrium so the cell is in homeostasis
2. Hypotonic Solution
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The concentration of dissolved substances is lower outside the cell
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A cell placed in a hypotonic solution, osmosis will cause water to move through the plasma membrane into the cell
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As water diffuses in the cell swells
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Cytolysis
– cell swelling
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This is what causes plants to be firm
2

3. Hypertonic Solution
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The concentration of dissolved substance is higher outside the cell
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If a cell is placed in a hypertonic solution, osmosis will cause water to leave the cell
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Cell will shrivel
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Plasmolysis – cell shrinking
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This is what causes plants to
Facilitated Diffusion
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Cell membranes have protein channels that act as carriers, making it easy for certain molecules to cross
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Facilitated Diffusion – transport materials across the cell membrane by means of transport proteins from high to low concentration
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Common in the movement of sugars and amino acids
Active Transport
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Active Transport
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Materials move from low to high concentration – against concentration gradient
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Requires energy
 Endocytosis – A cell surrounds and takes in material. (pac-man)
 Phagocytosis – large solid particles taken in by endocytosis.
 Pinocytosis
– liquid particles taken in by endocytosis.

Exocytosis
– material is released from cell. Cell excretes.
7-4 The Diversity of Cellular Life
Cell Differentiation
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The differences among living things arise from the ways in which cells are specialized to perform certain tasks
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Animal cells are specialized in many ways
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Red blood cells transport oxygen
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Cells in the pancreas produce proteins
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Muscle cells allow movement
3

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Guard cells in plants control the opening and closing of the stomata which allows
CO
2
, oxygen, water, in and out of plant
Levels of Organization
☺ The levels of organization in a multicellular organism are…
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Individual cells
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Tissues
– a group of similar cells
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Organs – groups of tissues that work together
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Organ Systems – a group of organs that work together
10-1 Cell Growth
Surface Area to Volume Ratio

Cells come in a variety of sizes

Range from 2-200
 m
 Why can’t most organisms be just one giant cell?
 You know the plasma membrane allows a steady supply of nutrients to enter cell and allows wastes to leave
 Diffusion becomes slow and inefficient as the distances become larger
 Cells would die before nutrients could reach them
 The cell cannot survive unless there is enough DNA to support the protein needs of the cell
 Surface area to volume ratio
 As cell size increases its volume increases much faster than its surface area

If cell size doubled the cell would require more nutrients and have more waste but the surface area would not have increased enough to get the nutrients and get rid of waste, so the cell would starve
4

7-3 Cell Boundaries
 A cells survival depends on its ability to maintain homeostasis and get nutrients
 Homeostasis
–
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Cell Membrane
☺
Regulates what enters and leaves the cell
☺
Selective Permeability –
☺
Made of a phospholipid bilayer –
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Phospholipid
–
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The two fatty acid tails ____________ water and the phosphate heads ________
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Water soluble molecules will not easily move through the membrane because they are stopped by the _________ __________ __________
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Fluid Mosaic Model
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Fluid because
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Mosaic because
5

☺
Transport Proteins
☺
☺
Allow needed substances or waste materials to move through plasma membrane
Passive Transport
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Passive transport
–
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3 Types of Passive Transport
1.
2.
3.
Diffusion
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Diffusion –
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Diffusion is a _______ process because it relies on the random motion of molecules
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Dynamic Equilibrium
–
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Concentration Gradient –
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Diffusion will continue until there is no _______________ ____________
6

☺
3 Factors That Affect Diffusion
1. Concentration
–
2. Temperature
–
3. Pressure –
Osmosis
☺
Osmosis –
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3 Types of Solutions Cells Can Be In
1. Isotonic Solution
☺
☺
Most solutions injected into the body are isotonic, so that cells are not damaged by the loss or gain of water
☺
The concentration of dissolved substances is in equilibrium so the cell is in
_______________
2. Hypotonic Solution
☺
☺
A cell placed in a hypotonic solution, osmosis will cause water to move through the plasma membrane into the cell
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As water diffuses in the cell ____________
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Cytolysis –
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This is what causes plants to be ___________
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3. Hypertonic Solution
☺
☺
If a cell is placed in a hypertonic solution, osmosis will cause water to
____________ the cell
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Cell will ____________
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Plasmolysis –
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This is what causes plants to __________
Facilitated Diffusion
☺
Cell membranes have protein channels that act as carriers, making it easy for certain molecules to cross
☺
Facilitated Diffusion –
☺
Common in the movement of sugars and amino acids
Active Transport
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Active Transport
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Materials move from low to high concentration –
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Requires ____________
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
Endocytosis
–
 Phagocytosis –
 Pinocytosis –
 Exocytosis
–
7-4 The Diversity of Cellular Life
Cell Differentiation
☺
The differences among living things arise from the ways in which cells are specialized to perform certain tasks
☺
Animal cells are specialized in many ways
☺
Red blood cells ____________ ___________
☺
Cells in the pancreas produce ____________
☺
Muscle cells allow _______________
☺
Guard cells in plants control the opening and closing of the stomata which allows
CO
2
, oxygen, water, in and out of plant
Levels of Organization
☺ The levels of organization in a multicellular organism are…
☺
Individual cells
☺
Tissues –
☺
Organs
–
☺
Organ Systems –
9

10-1 Cell Growth
Surface Area to Volume Ratio
 Cells come in a variety of sizes
 Range from ____________
 Why can’t most organisms be just one giant cell?
 You know the plasma membrane allows a steady supply of nutrients to enter cell and allows wastes to leave
 Diffusion becomes __________ and inefficient as the distances become _________
 Cells would die before nutrients could reach them
 Surface area to volume ratio
 As cell size increases its ____________ increases much faster than its
__________ __________
 If cell size doubled the cell would require more nutrients and have more waste but the surface area would not have _______________ enough to get the nutrients and get rid of waste, so the cell would starve
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