Cell Transport

Biology 11

• Two parts of a Solution:

–Solute• A substance dissolved in another substance,

usually in lesser amount.

–Solvent• A substance in which another substance is

dissolved, forming a solution

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• Cell membranes are selectively permeable. This means that some things can pas through while others cannot.

• Proteins embedded in the cell membrane are used as channels and pumps which allow substances through or not.

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Cell TransportCell Transport

Diffusion• Diffusion is the movement of molecules from an

area of high concentration to an area of lower concentration.

Cell Transport

• There are three types of cell transport:

– Simple Diffusion

– Facilitated Diffusion

– Active Transport

Passive Transport

• Passive Transport: Movement of materials across the cell membrane going with the concentration gradient (from a region of greater concentration to a region of lesser concentration).

Simple Diffusion and Facilitated Diffusion are both examples of Passive Transport

• *Cell uses no energy to transport particles!

Simple Diffusion

• No transport protein used• Movement with the concentration gradient (high

to low)• No additional cell energy required

• Examples: • water, • oxygen,• carbon dioxide.

Homeostasis

• To maintain a stable, constant condition.

• To maintain equilibrium.

• The cell wants its internal environment to be the same as its external environment.

Concentration Gradient

• When there is a difference in concentrations:– High concentration means more particles– Low concentration means less particles

– In diffusion, particles move from a high concentration to a low concentration to reach on EQUAL concentration (equilibrium) on each side.

Passive Transport Examples

• a) Osmosis – specific type of diffusion (can you remember the definition??)

• b) Facilitated diffusion – Process by which molecules diffuse across a cell membrane with the aid of transport proteins. This is for particles that cannot dissolve into the lipid bi-layer or are too large to pass through.

PassiveTransport

• A solution that has the same concentration of solutes as the cell.

• Therefore there is no net movement of water molecules

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Hypertonic

• The solution has higher concentration of solutes then the cell.

• Therefore there will be a net movement OUT of the cell.

• A solution that has a lower concentration of solutes than the cell.

• There will be a net movement of water into the cell.

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Hypotonic

Osmotic Pressure

• This is the pressure that water exerts on the hypertonic side of a selectively permeably membrane.

• It can be problematic for living cells because they can burst from over-inflation with water or shrivel up from loss of water.

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Cytolysis: The bursting or rupture of a cell.

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Facilitated Diffusion

• Transport protein used: carrier protein or channel protein

• Movement with the concentration gradient

• No additional cell energy required

• Passive

• Example: glucose molecules

Facilitated Diffusion

• Similar to simple diffusion in the sense that it is diffusion (across a membrane) from a high concentration to a lower concentration.

• However, this time the rate of diffusion is greatly accelerated by the action of membrane proteins that act as carrier molecules and aid in diffusion.

Facilitated Diffusion

Protein Channels Carrier Proteins

• Passive Transport Video

Active Transport

• Molecular Active Transport: Movement of materials across the cell membrane going against the concentration gradient (from a region of lesser concentration to a region of greater concentration).

• *Requires energy from cell!

Active Transport

• Transport protein used: Carrier Protein

• Movement AGAINST the concentration gradient (low to high)

• Additional cell energy required

• Active

• Example:

Sodium Potassium Pump

Active Transport

• Molecular active transport involves protein pumps.

• Examples of active transport:– Cells in Gills of marine fish actively pump out

salts.– Root cells of plants often take in large

quantities of ions.

• Active transport Video

Sodium Potassium PumpActive Transport

Bulk Membrane Transport

• Active transport (requires energy)

• Requires the creation of vacuoles and vesicles

• Two types:– Endocytosis– Exocytosis

Animation

Endocytosis• Endocytosis: The process by which the plasma

membrane engulfs and takes in substances from a cell’s environment. *Common in unicellular organisms.

• 2 types:– i) Phagocytosis: Form of endocytosis in which large

solid particles are taken into the cell. Example – WBC’s engulfing harmful bacteria

– ii) Pinocytosis: Form of endocytosis in which small liquid droplets are taken into the cell. a.k.a. cell drinking

Endocytosis

Phagocytosis

Exocytosis

• Exocytosis: Cell products or wastes are enclosed in vesicles and released to outside of cell.

• Process:– Golgi Apparatus “packages” the material into a vesicle and

sends it to the cell membrane– The vesicle fuses with the membrane– The material is deposited outside the cell

*Reverse process of endocytosis.

• Examples = secretion or elimination of waste

Energy and Life

Photosynthesis and Respiration

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What is energy?• Energy is the capacity to do work.

• All living this require energy, but how do they get it?

• There are two ways to receive energy,– Produce it– Consume it

Photosynthesis

• The sun is the main source of energy for the earth.

• Autotrophs make their own food, and most are green plants.

• This is done through the process of Photosynthesis.

Photosynthesis

• We know photosynthesis requires energy from the sun, but the sun is not available 24 hours a day!

• Photosynthesis must occur in two phases:– Light dependent reactions

• Convert light energy into chemical energy (ATP and NADPH)

– Light independent reactions• Uses ATP and NADPH from the light dependent

reactions to build glucose.

Role of Photosynthesis• Plants use it to make food

• Animals get their food from plants, so therefore, from photosynthesis as well (consumers)

• Photosynthesis also produces oxygen which most living things need to respire and live.

The process of photosynthesis

• Light is trapped by chlorophyll and provides energy for photosynthesis

• Sunlight energy is used to split water in half (photolysis)

The process of photosynthesis

• Products from splitting water:– Protons stored for later use– Electrons Passed to chorophyll– Oxygen can be used in respiration or

release

• Light energized the electrons and turns them into high energy electrons. These are passed down an electron transport chain

Electron Transport Chain

• Is a series of proteins on the thylakoid membrane of chloroplasts.

• Electrons are passed from one protein to another, and energy is released which:– Helps join ADP and phosphate to form ATP– Allows hydrogen to join with NADP to form

NADPH– Both forms of energy are used in light

independent reactions.

Process of Photosynthesis

• Glucose is formed when the high energy electrons, protons from storage and carbon dioxide from air are combined.

• This is takes place in chloroplasts and is known as the Calvin Cycle. This is a part of the light independent reactions.

The Calvin Cycle• 1. Grab: A five-carbon carbon catcher catches

one molecule of carbon dioxide and forms a six-carbon molecule.

• 2. Split: the enzyme RuBisCO (with the energy of ATP and NADPH molecules) breaks the six-carbon molecule into two equal parts.

• NADP (nicotinamide adenine dinucleotide phosphate) is a coenzyme that carries electrical energy used in cellular processes.

The Calvin Cycle• 3. Leave: A trio of three carbons leave and

become sugar. The other trio moves on to the next step.

• 4. Switch: Using ATP and NADPH, the three carbon molecule is changed into a five carbon molecule.

• 5. The cycle starts over again

Photosynthesis• Once sugars are created through the calvin cycle,

mitochondria can now use it for cellular respiration.

• The mitochondria uses glucose, or sugars, to create ATP which is a usable energy for the cell.

• This not only occurs in plant cells, but in our own cells as well. By consuming other plants and animals, our body uses the sugars ( carbohydrates) that we eat into usable energy by mitochondra.

Review Questions

• What is the primary function of photosynthesis?

• Name two molecules that are produced during the light dependent reactions of photosynthesis and serve as temporary sites for energy storage.

• In eukaryotic cells, photosynthesis occurs in organelles named?

• True or False The Calvin cycle (= light-independent reactions) can occur in a plant that is in dark room so long as the materials carbon dioxide, ATP, and NADP-H are present.

Cellular Respiration

• Process by which mitochondria break down food molecules to produce ATP in plants and animals.

• Nutrients + Oxygen Water + ATP + CO2

Cellular respiration

• Changes organic chemical energy (glucose) into inorganic chemical energy (ATP)

• Three stages of cellular respiration– Glycolosis

• Anaerobic ( does not require oxygen)

– Krebs Cycle• Aerobic ( requires oxygen)

– Electron Transport Chain• Aerobic (requires oxygen)

Glycolysis

• Breaks down glucose into two molecules of pyruvic acid

• Uses enzymes and takes place in the cytoplasm of the cell

• Produces– 2 pyruvic acid molecules – used in next step

of cellular respiration– 2 ATP molecules –energy for the cell– 2 NADH – electron carrier

• Before the next step of cellular respiration, the pyruvic acid molecules formed in the glycolysis must go into the mitochondria.

• The next two aerobic reactions will then form:

Pyruvic acid CO2 + Water + ATP

Krebs Cycle

• Is a series of chemical reactions used by all aerobic organisms to generate energy.

• Provides the hydrogen and electrons needed for the electron transport chain, which happens in the mitochondria.

Krebs Cycle

• The following is formed during the Krebs Cycle:

– 2 Molecules of CO2 are released– 2 Molecules of ATP are formed– 3 molecules of NAD+ are combined with

hydrogen ( NAD+ NADH)– 1 molecule of FAD+ combines with hydrogen

( FAD+ FADH)

Electron Transport Chain

• Following the Krebs cycle, the electron transport chain uses the electron carriers (NADH and FADH2) to pass electrons down a protein chain and slowly releases energy that is used to form ATP and water molecules.

• This transfers the most energy.

Equation

Summary

• Photosynthesis- Converts solar energy into chemical energy

• Cellular Respiration – Converts chemical energy into usable energy

• Therefore living things deal with three types of energy!– Solar energy– Chemical energy (sugars / lipids)– Usable energy (A.T.P.)

Review Questions• What are the three main processes of Cellular

Respiration?

• What is produced during glycolysis?

• Name two electron carriers.

• Compare and contrast:– Anaerobic and aerobic– Photosynthesis and Cellular respiration