Chapter 5 Notes (from power-point)
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The cell in action
Exchange with the environment
Cells need to bring in & take out things in the cell.
A. What is diffusion?
• Diffusion = the movement of particles from an are where the concentration is
high to an area where the concentration is low.
• This movement can occur across the cell membrane or outside of cells.
Exchange with the environment
Diffusion of water:
• Osmosis = the diffusion of water through the cell membrane.
• Think: water moves to areas of high concentration of particles.
• All organisms need water to live.
The cells of living organisms are surrounded by & filled with fluids that are made mostly
of water.
Exchange with the environment
The Cell & osmosis:
• Human red blood cells (RBC) are normally surrounded by blood plasma, which is
made up of water, salts, sugars, & other particles in the same concentration as
they exist inside the RBCs.
• The shape of the RBCs is affected by the concentration of water outside the cell:
• 3 types: hypotonic, hypertonic, & isotonic solutions.
Exchange with the environment
Hypotonic solution = the solution has a low solute concentration than the cell, so water
moves into the cell causing plant & animal cells to swell & burst.
Isotonic solution = the concentration of solutes is equal inside & outside the cell so
water moves across the membrane in both directions maintaining cell size.
Hypertonic = the solution has a higher solute concentration than the cell so water
moves out of the cell & into the solution causing the cell to shrink.
Exchange with the environment
B. Moving small particles:
Many particles, such as water & oxygen can diffuse directly through the cell membrane,
which is made of phospholipid molecules.
• These particles can slip through the membrane because of their small size.
Larger molecules cannot pass through this way.
• Ie: sugar & amino acids ae not small enough to squeeze between the
phospholipid molecules & they are also repelled by the phospholipids in the
membrane.
• Must travel through the “protein doorways” located in the cell membrane to
enter or exit the cell.
• Particles can travel through these proteins by passive transport or active
transport.
Exchange with the environment
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Passive transport (facilitated diffusion)= the diffusion of particles through the proteins.
• Particles move from an area of high concentration to an area of low
concentration.
• Cell does not need to use energy to make it happen.
Active transport = the movement of particles through proteins against the normal
direction of diffusion.
• Particles are moved from an area of low concentration to an area of high
concentration.
• The cell must use energy to make this happen.
Exchange with the environment
C. Moving Large Particles:
• 2 ways: endocytosis & exocytosis.
• Endocytosis = the cell membrane surrounds a particle & encloses it in a vesicle.
• This is how particles, such as other cells, can be brought into the cell.
• Steps:
• 1. the cell comes into contact with a particle.
• 2. the cell membrane begins to wrap around the particle.
• 3. once the particle is completely surrounded, a vesicle pinches
off.
• Exchange with the environment
Exocytosis = vesicles are formed at the endoplasmic reticulum or golgi complex & carry
the particles to the cell membrane.
Steps:
• 1. large particles that must leave the cell are packaged in vesicles.
• 2. the vesicle travels to the cell membrane & fuses with it.
• 3. the cell releases the particles into its environment.
Cell energy
Why do you get hungry?
• Hungry is your body’s way of telling you that your cells need energy.
A. From sun to cell:
• Nearly all energy that fuels life comes from the sun.
• Your cells get energy from the food that you eat.
• Like many other kinds of organisms, you must eat plants or organisms that have
eaten plants.
• Plants go through photosynthesis = process by which plants are able to capture
light energy from the sun & change it into food.
• Photosynthesis = “made by light.”
• Without plants & other producers, consumers would not be able to live.
Cell energy
Photosynthesis:
• Chlorophyll = main pigment used in photosynthesis; gives plants their green
color.
• In the cells of plants, chlorophyll is found in chloroplasts.
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Plants used energy captured by chlorophyll to change carbon dioxide (CO2) &
water (H2O) into food (food produced is simple sugar glucose C6H12O6). Oxygen
(O2) is produced as a waste product for plants.
Photosynthesis equation:
• Happens in the leaf of a plant -> plant cell -> chloroplast.
• 6CO2 + 6H2O + light energy  C6H12O6 + 6O2
Cell energy
B. Getting energy from food:
• Food has to be broken down so that the energy it contains can be converted into
a form your cells can use.
2 ways to break down energy:
• 1. cellular respiration.
• 2. fermentation.
Cell energy
1. Cellular Respiration:
• Different than respiration = “breathing.”
• Breathing supplies your cells with oxygen needed to perform cellular respiration.
• Breathing also rids your body of CO2, which is a waste product of cellular
respiration.
Cellular respiration = glucose (food) is broken down into CO2 & H2O & energy is
released.
• ATP us the stored energy, but the energy released in cellular respiration is in the
form of heat.
• This heat helps maintain body temperature.
• In the cells of plants, animals, & other prokaryotes, cellular respiration takes
place in mitochondria.
Cellular respiration formula: C6H12O6 + 6O2  6CO2 + 6H2O + energy (ATP)
Cell energy
2. Fermentation:
• Ie: have you ever run so far that you started to feel a burning sensation in your
muscles?
• Sometimes your muscle cells cannot get the oxygen they need to produce ATP by
cellular respiration.
• When this happens, they use the process of fermentation.
Fermentation = leads to the production of a small amount of ATP & products from the
partial breakdown of glucose.
• 2 types:
• 1. first type occurs in muscles. It produces lactic acid, which contributes to
muscle fatigue after strenuous activity. It occurs in muscle cells of other animals
& in some types of fungi & bacteria.
• 2. 2nd type occurs in certain types of bacteria & yeast.
The cell cycle
Cells replaced often by new cells in your body.
A. The life of a cell:
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Cell cycle = the life cycle of a cell.
Begins when a cell is formed & ends when the cell divides & forms new cells.
Before cell divides, it makes a copy of its DNA & other materials that are needed
to carry out the processes of life.
• DNA = contains the info that tells a cell how to make proteins.
• DNA is organized into structures called chromosomes.
• Copying chromosomes ensures that each new cell will have all the
tools needed for survival.
The cell cycle
Making more prokaryotic cells:
• Binary Fission = splitting into 2 parts.
• Each resulting cell contains 1 copy of DNA.
• Simple reproducing these cells because these are simple cells: have ribosomes &
a single, circular chromosome, but they do not have membrane covered
organelles.
The cell cycle
Eukaryotic Cells & their DNA:
• Much larger & more complex than prokaryotic cells.
• Eukaryotic cells have much more DNA.
• For eukaryotic cells, the number of chromosomes in cells differs from 1 organism
to the next & does not relate to the complexity of the organism:
• Ie: fruit flies = 8 chromosomes
• Potatoes = 48 chromosomes
• Humans =46 chromosomes (23 pairs)
• Homologous chromosomes = pair of similar chromosomes.
The cell cycle
Making more Eukaryotic Cells:
Cell cycle includes 3 stages:
Stage 1: cell grows & copies its organelles & chromosomes.
• DNA & proteins are loosely coiled pieces of thread.
• After chromosomes are duplicated, 2 copies are held together at a region
called the centromere & are called chromatids.
• Chromatids twist, coil, & condense into a x shape.
Stage 2: chromatids separate; process known as Mitosis.
• Mitosis ensures that each new cell receives a copy of each chromosome.
• Mitosis has 4 phases.
Stage 3: cell divides & produces 2 cells that are identical to the original cell.
• The cell cycle
Mitosis steps:
Before mitosis: Chromosomes & cell materials copied. Centrioles copied. Each
chromosome now consist of 2 chromatids.
1. nuclear membrane breaks apart, 2 centrioles move to opposite side of a cell, & fibers
form between 2 pairs of centrioles & attach to centromeres.
2. chromosomes line up along the equator of the cell.
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3. chromatids separate & are pulled to opposite side of the cell by fibers attached to
centrioles.
4. nuclear membrane forms around 2 sets of chromosomes & they unwind, fibers
disappear, & Mitosis is completed.
The cell cycle
Cytokinesis (after Mitosis):
Cytoplasm splits into 2: result is 2 identical cells that are identical to the original cell
from which they were formed.
Plant cells (have cell wall): when plant cells divides, a cell plate forms in the middle &
grows toward the edge until the cell splits into 2.