1. Essentials of Biology Sylvia S. Mader
Chapter 5
Lecture Outline
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2. 5.1 What Is Energy? Energy is the capacity to do work.
Our biosphere gets its energy from the sun.
2 basic forms of energy
Potential energy – stored energy
Kinetic energy – energy of motion
2 forms are converted back and forth

3. Measuring energy Two energy laws Food energy measured in calories
calorie – amount of heat required to raise temperature of 1 gram of water by 1°C
Kilocalorie or Calorie = 1,000 calories
Value listed on food packages
Two energy laws
First law – Conservation of energy
Energy cannot be created or destroyed, but it can be changed from one form to another
Second Law
Energy cannot be changed from one form to another without a loss of usable energy
Heat is the least usable form of energy

4. 5.2 ATP: Energy for Cells Adenosine triphosphate
Energy currency for cells
Cells use ATP to carry out nearly all activities
One nucleotide along with
3 phosphate groups makes it unstable
Easily loses a phosphate group to become ADP (adenosine diphosphate)
Continual cycle of breakdown and regeneration

5. Figure 5.3 ATP adenosine triphosphate (ATP) P P P
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adenosine
triphosphate (ATP) P P P

6. ATP releases energy quickly
Figure 5.4 The ATP cycle
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ATP
energy released during
cellular respiration
energy for cellular work
(e.g., protein synthesis,
muscle contraction)
ADP + P
ATP releases energy quickly
Amount of energy released is usually just enough for a biological purpose
Breakdown can be easily coupled to an energy-requiring reaction

7. Flow of energy
Activities of chloroplasts and mitochondria enable energy to flow from the sun through all living things
Photosynthesis – solar energy used to convert water and carbon dioxide into carbohydrates
Food for plants and other organisms
Cellular respiration – carbohydrates broken down and energy used to build ATP
Useful energy is lost with each transformation
Living things dependent on constant in/out of solar energy

8. (plant): © Comstock/PunchStock RF; (woman): © Getty RF
Figure 5.6 Flow of energy
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Energy Conversions
heat
solar
energy
chloroplast O2
Chemical energy
(carbohydrate)
CO2 and H2O
mitochondrion
heat
Chemical work
Transport work
Mechanical work
ATP
(plant): © Comstock/PunchStock RF; (woman): © Getty RF

9. Humans dependent on cycling of molecules between plants and animals
Figure 5.7 Energy of life
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Potato
Fruit
Grain
Meat
Potatoes contain about 90 Calories
per 3.5 oz (100 g)
Potatoes contain starch, which stores
energy for the growing plant. When a
potato is eaten, starch molecules are
broken down to simple sugars in the
body before their energy is released.
Apples contain about 60 Calories per
3.5 oz (100 g)
Fruits such as apples contain natural
sugars that provide energy. The body
converts excess sugar into fat, which
is stored energy that can be used
later.
Grain contains about 300 Calories per
3.5 oz (100 g)
Grain is an efficient energy source
because it directly stores the energy of
photosynthesis. Grains are a good
source of energy for humans and
animals.
Pork chops, grilled or broiled, contain
about 215 Calories per 3.5 oz (100 g)
Meat is a good energy source; much
of its energy is stored in fat. However,
meat isn’t an efficient energy source
because only a small amount of the
energy taken in by a living pig, for
example, is converted to energy
usable by the human or animal that
eats the pork chop.
(potato, grain): © The McGraw-Hill Companies, Inc./John Thoeming, photographer; (fruit): © Getty RF; (meat): © Foodcollection/Getty RF
Humans dependent on cycling of molecules between plants and animals
Inhale oxygen, eat plants and animals
Energy rich foods allow us to produce the ATP required to maintain our bodies and carry on activities

10. A LOWER hurdle is easier/ faster to get over
Figure 5.10 Energy of activation
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without
enzyme
A LOWER hurdle is easier/ faster to get over
A LOWER energy of activation makes a reaction easier/ faster
energy of activation
(more needed)
with
enzyme
energy of
activation
(less needed)
reactant
Potential Energy
product
Reaction

11. 5.4 Cell Transport
Plasma membrane regulates traffic in and out of cell.
Selectively permeable – some substances pass freely, some transported, some prohibited
3 ways to enter
Passive transport – substances move from higher to lower concentration, no additional energy required.
Active transport – substances move from lower to higher concentration, additional energy is required.
Bulk transport – movement independent of gradients, additional energy required.

12. Passive transport Non membrane required for simple diffusion
Molecules move down their concentration gradient until equilibrium is reached
Cell does not expend additional energy – molecules already in motion
Some molecules slip between phospholipids
Facilitated diffusion – others use transport protein specific to molecule
Water uses aquaporins – explains faster than expected transport rate

13. Figure 5.11 Simple diffusion demonstration
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red dye
Time
H2O
membrane a. b.
Net movement of dye is to the left side of membrane
At equlibirum, dye equal on both sides of membrane and net movement stops
Solution – contains solute (dye or other substance) and solvent (water)

14. Effect of osmosis on cells
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Red blood cells
Effect of osmosis on cells
Isotonic solution
Cell neither gains or loses water
Concentration of water same on both sides of the membrane
0.9% saline isotonic to red blood cells
normal cells
Isotonic
solution
normal cell
Figure 5.13 Osmosis in animal and plant cells
Plant cells

15. Copyright © The McGraw-Hill Companies, Inc
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Hypotonic solution
Concentration of water outside cell greater than inside cell
Cell gains water
Animal cells may lyse or burst
Plant cells use this to remain turgid
cells swell, burst
Hypotonic
solution
normal turgid cell

16. Figure 5.13
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Hypertonic solution
Concentration of water outside cell less than inside cell
Cell loses water
Animal cells shrink
Plant cells undergo plasmolysis and may wilt
shriveled cells
Hypertonic
solution
cytoplasm shrinks
from cell wall

17. Figure 5.14 Active transport
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transport
protein
ATP P
Outside
Inside P
Active transport
Cells expend energy to move molecules against a concentration gradient
Requires transport protein
Sodium-potassium pump important in maintaining gradient of ions used in nerve impulse conduction

18. Bulk Transport
Macromolecules are often too large to be moved by transport proteins
Vesicle formation takes them in or out of cell
Exocytosis – movement out of cell

19. Figure 5.15a Exocytosis plasma membrane Inside a. Exocytosis
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plasma membrane
Inside
a. Exocytosis

20. Endocytosis – movement into cell
Phagocytosis – cell surrounds, engulfs and digests particle.
Pinocytosis – vesicle form around liquid or small particles.
Receptor-mediated endocytosis – receptors for particular substances found in coated pit – selective and more efficient.

21. Figure 5.15b Endocytosis Inside b. Endocytosis
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Inside
b. Endocytosis

22. Figure 5.16 Receptor-mediated endocytosis
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coated
vesicle
coated
pit
receptor
protein
molecule
(both): Courtesy Mark Bretscher