Chapter 1 Biology : Exploring Life

1.1 All forms of life share common propertiesBiology is the scientific study of life.*7 properties and processes that we associate with life:

Order Reproduction Growth and Development Energy Processing Response to the environment Regulation Evolutionary Adaptation

1.2 In life’s hierarchy of organization, new properties emerge at each level

o Biosphere – all of the environments that support lifeo Ecosystem – all of the organisms living in a particular areao Community - the entire array of organisms in an ecosystemo Population – all the individuals of a particular species living in an areao Organism – an individual living thingo Organ System – consists of several organs that cooperate in a specific functiono Organ –made up of a group of similar cells that perform specific functiono Tissue – organs are made up of tissueso Cell – fundamental unit of lifeo Organelle – membrane-enclosed structure that performs a specific function in a cello Molecule – cluster of small chemical units called atoms held together by chemical bonds

Emergent properties result from the interactions among component parts.

1.3 Cells are the structural and functional units of life

The cell is the level at which the properties of life emerge.

Cell Theory - All organisms are made up of cells. All Cells share many characteristics.

2 Basic Types of Cells:

Eukaryotic Cells – 2.1 billon years ago-membrane-enclosed organelles, including a nucleus containing DNA

Prokaryotic Cells – 1.5 billion years of life on Earth-smaller and lack such organelles

1.4 Organisms interact with their environment, exchanging matter and energy

1.5 The unity of life is based on DNA and a common genetic codeEvolution is the core theme of BiologyDNA – responsible for hereditary and for programming the activities of a cell

1.6 The diversity of life can be arranged into three domains.Diversity is a hallmark of life.The 3 domains of Life:

Bacteria and Archea, consist of prokaryotes Eukarya – eukaryotic domain, includes various protists and

Kingdoms : Fungi, Plantae, and Animalia

1.7 Evolution explains the unity and diversity of life

Charles Darwin synthesized the theory of evolution by natural selection

1.8 Scientific inquiry is used to ask and answer questions about nature

Science is derived from a Latin verb meaning “to know”

Data may be qualitative or quantitative

Inductive reasoning – this kind of reasoning derives generalizations from a large number of specific observations

Hypothesis – is a proposed of explanation for a set of observation

Deductive reasoning – the logic flows from general premises to the specific results we should expect if the premises are true

Scientific Theory – is broad in scope, generated new hypotheses, and is supported by a large body of evidence

1.9 Scientists form and test hypothesis and share their results

Predictions can be tested by experiments. Results can either falsify or support the hypothesis.

In a controlled experiment, the use of control and experimental groups helps to demonstrate the effect of a single variable.

1.10 Biology, technology, and society are connected in important ways

Technologies advances stem from scientific research, and research benefits from new technologies.

1.11 Evolution is connected to our everyday lives

Evolutionary theory is useful in medicine, agriculture forensics, and conservation

Chapter 2 : The Chemical Basis of Life

2.1 Organisms are composed of elements, in combinations called compounds

Matter – anything that occupies space and has mass

Element – a substance that cannot be broken down to other substances by ordinary chemical means

Compound – substance consisting of 2 or more different elements combined in a fixed ratio

Oxygen, Carbon, Hydrogen, and Nitrogen – 96% of living matter

2.2 Trace elements are common additives to food and water

Iron – vital for energy processing and for transporting oxygen in blood Iodine – essential ingredient of a hormone produce by thyroid gland- Iodine deficiency = goiter

Fluoride – mouthwash & toothpaste

2.3 Atom consist of proton, neutrons, and electrons

Atom – indivisible, smallest unit of matter

Proton – positively charged Electron – negatively charged Neutron – neutral (no charge)

Atomic Number = Proton = Electron

Mass number = Protons+Neutrons = atomic mass

Isotope – of an element have the same # of protons but different numbers of neutrons

Radioactive isotopes – nucleus decays spontaneously, giving of particles and energy

2.4 Radioactive isotopes can help or harm us

Chemical Bonds

2.5 The distribution of electrons determines an atom’s chemical properties

Electron shells – electrons move around the nucleus only at certain energy levels

Chemical bonds – an atom whose outer electron shell is not full tends to interact with other atoms and share, gain, or lose electrons, resulting in attraction called chemical bonds

2.6 Covalent bonds join atoms into molecules through electron sharing

Covalent bond – 2 atoms share one or more pairs of out-shell electron

Nonpolar Covalent Bond – electrons are shared equally Polar Covalent Bonds – (in water), electrons are pulled closer to the more electronegative atom

2.7 Ionic bonds are attraction between ions of opposite charge

Ion – is an atom or molecule with an electrical charge resulting from a gain or loss of one or more electrons

2.8 Hydrogen bonds are weak bonds important in the chemistry of life

2.9 Chemical reactions make and break chemical bonds

Water’s Life-Supporting Properties

2.10 Hydrogen bonds make liquid cohesive

Cohesion – molecules stick together

2.11 Water’s hydrogen bonds moderate temperature

Heat – amount of energy associated with the movement of atoms & molecules

Temperature – intensity of heat

2.12 Ice is less dense than liquid water

Ice: hydrogen bonds are stable

Liquid Water: hydrogen bonds constantly break and re-form

2.13 Water is the solvent of life

Solution – liquid consisting of a uniform mixture of 2 or more substances

Solvent – dissolving agent

Solute – substance that is dissolved

2.14 The chemistry of life is sensitive to acidic and basic condition

Acid – compound that releases H+ in solution

Base – accepts H+

pH – (potential of hydrogen), describe how acidic or basic a solution is.

- 0= most acidic, 7= neutral, 14= most basic

2.15 Acid precipitation and ocean acidification threaten the environment

2.16 The search for extraterrestrial life centers on the search for water

Chapter 3 The Molecules of Cell

3.1 Life’s molecular diversity is based on the properties of carbon

Carbon-based molecules are called organic compounds.

Compounds composed of only carbon and hydrogen are called hydrocarbons. (methane, propane)

The chain of carbon atoms in an organic molecule is called a carbon skeleton.

Compounds with the same formula but different structural arrangements are called isomers.

3.2 A few Chemical groups are key to the functioning of biological molecules

Hydroxyl group consists of a hydrogen atom bonded to an oxygen atom.

Carbonyl group, a carbon atom is linked by a double bond to an oxygen atom.

Carboxyl group consists of a carbon double-bonded to an oxygen atom and also bounded to a hydroxyl group.

Amino group has a N bonded to two H and the C skeleton.

Phosphate group consists of a P atom bonded to four O atoms.

Methyl group consists of a carbon bonded to three hydrogens.

3.3 Cells make a huge number of large molecules from a limited set of small molecules

Four main classes of molecules; carbohydrates, lipids, proteins, and nucleic acids

Macromolecules; carbohydrates, proteins, and nucleic acids

Cells make most of their macromolecules by joining smaller molecules into chains called polymers. (many, part)

Polymer is a large molecule consisting of many identical or similar building blocks strung together.

The building blocks of polymers are called monomers.

Cells link monomers together to form polymers by a dehydration reaction, a reaction that removes a molecule of water.

Digestion process is called hydrolysis; means to break (lyse) with water (hydro-).

3.4 Monosaccharides are the simplest carbohydrates.

The carbohydrate monomers (single-unit sugars) are monosaccharides

Glucose are the main fuel molecules for cellular work.

3.5 Two monosaccharides are linked to form a disaccharide.

3.7 Polysaccharides are long chains of sugar units.

Starch, a storage polysaccharide in plants.

Glycogen, storage polysaccharide of animals.

Cellulose, most abundant organic compound on Earth. Found in plant cell walls.

Chitin, a component of insect exoskeletons and fungal cell walls.

3.8 Fats are lipids that are mostly energy-storage molecules

Lipids are diverse, hydrophobic compounds composed largely of carbon and hydrogen.-don’t form polymers

Fats (triglycerides) – consist of glycerol linked to 3 fatty acids. Saturated fatty acids – found in animal fats Unsaturated fatty acids – are typical of plant oils

3.9 Phospholipids and steroids are important lipids with a variety of functions.

Cells could not exist without phospholipids; components of cell membranes

Steroids include cholesterol and some hormones

Cholesterol – common component in animal cell membranes.

3.10 Anabolic steroids pose health risks

Anabolic steroids are synthetic variants of the male hormone testosterone.

3.11 Proteins are made from amino acids linked by peptide bonds

Protein is a polymer of amino acids.

Protein diversity is based on different sequences of amino acids, monomers that contain an amino group, a carboxyl group, an H group , and an R group, all attached to a central carbon.

Peptide bond – covalent linkage

Polypeptide – additional amino acids are added by the same probes to form a chain of amino acids.

3.12 A protein’s specific shape determines its function

3.13 A protein’s shape depends on four levels of structure

Primary Structure – is the sequence of amino acids in its polypeptide chain Secondary Structure – is the coiling or folding of the chain, stabilized by hydrogen bonds. Tertiary structure – is the overall three-dimensional shape of polypeptide Quaternary structure – proteins made of more than one polypeptide

3.14 DNA and RNA are the two types of nucleic acids

Gene consists of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid)

DNA and RNA serve as the blueprints for proteins and thus control the life of a cell.

3.15 Nucleic acids are polymers of nucleotides

The monomers that make up nucleic acids are nucleotides

Nucleotides are composed of a sugar, a phosphate group, and a nitrogenous base.

3.16 Lactose tolerance is a recent even in human evolution

Chapter 4 : A Tour of the Cell

4.1 Microscopes reveal the world of cell

Light Microscope (LM) – visible light is passed through a specimen and then through glass lenses

Electron Microscope (EM)– focuses beam of electrons through a specimen

Scanning electron microscope (SEM) – study the detailed architecture of cell surfaces Transmission electron microscope (TEM) – study the details of internal cell structure

Magnification – the increase in the apparent size of an object

Paramecium – single-celled protest

Cell theory – All living things are composed of cells and that all cells come from other cells

4.2 The small size of cells relates to the need to exchange materials across the plasma membrane

Plasma Membrane – forms a flexible boundary between the living cell and its surroundings

4.3 Prokaryotic cells are structurally simpler then eukaryotic cells

Eukaryotic Cells – membrane-enclosed nucleus, with organelles

- eukaryote means true nucleus- Animal Cell and Plant cell

Prokaryotic cells – much smaller & simpler than eukaryotic cells, no nucleus or other membrane-bound organelles

- Prokaryote means before nucleus- Domain Bacteria and Archaea

All cells have several basic features in common:

o Plasma Membraneo Chromosomes – carrying genes made of DNAo Ribosomes – make proteins according to instructions from the geneso Cytoplasm – interior of both cells

4.4 Eukaryotic cells are partitioned into functional compartments

Organelles – “little organs”, perform specific functions in the cell

Basic Functional Groups:

1) The nucleus & ribosomes – carry out the genetic control of the cell2) The endoplasmic reticulum, Golgi Apparatus, lysosomes, vacuoles, and peroxisome

– manufacture, distribution, and breakdown of molecules3) Mitochondria & chloroplasts (plant cell) – energy processing4) Cytoskeleton, Plasma Membrane, & plant cell wall – structural support, movement, and

communication

Cellular metabolism – chemical activities of cells

Not found in animal cells: Central Vacuole, chloroplast, cell wall, plasmodesma

ANIMAL CELL

PLANT CELL

Not found in plant cells:

Lysosomes & centrioles

Cell

Wall – protect cells and help maintain their shape Plasmodesma – cytoplasmic channels through cells walls that connect adjacent cells Chloroplasts – where photosynthesis occurs Large Central vacuole – a compartment that stores water & a variety of chemicals

4.5 The nucleus is the cell’s genetic control center

Nucleus – contains most of the cell’s DNA (master plans)- Controls the cell’s activities by directing protein synthesis- Houses the cell’s DNA and directs protein synthesis by making messenger RNA Chromatin – complex of proteins and DNA Nuclear Envelope – a double membrane enclosing the nucleus Endoplasmic Reticulum – cell’s network of membranes Nucleolus – in the nucleus, where ribosomal RNA (RNA)is synthesized

4.6 Ribosomes make proteins for use in the cell and for export

Ribosomes – synthesize proteins according to the instructions carried by messenger RNA from the DNA in the nucleus

The Endomembrane System4.7 Many cell organelles are connected through the endomembrane system

Endomembrane System – many of the membranes of the eukaryotic cell are part of this

Vesicles – sac made of membrane in the cytoplasm of a eukaryotic cell

4.8 The endoplasmic reticulum is a biosynthetic factory

Endoplasmic reticulum – extensive network of flattened tubes and sacs

- Endoplasmic means “within the cytoplasm”, reticulum mean “little net”

Smooth ER – lacks attached ribosomes- synthesizes lipids and processes toxins

Rough ER – has ribosomes that stud the outer surface of the membrane- manufactures membranes, and ribosomes on its surface produce membrane and secretory proteins

4.9 Golgi apparatus finishes, sorts, and ships cell products

Golgi apparatus – consists of stacks of sacs that modify ER products and ship them to other organelles

4.10 Lysosomes are digestive compartments within a cell

Lysosomes – membranous sac of digestive enzymes

- house enzymes that function in digestion and recycling within the cell

4.11 Vacuoles function in the general maintenance of the cell

Plant cell contain a large central vacuole that stores molecules and wastes and facilitates growth

4.12 A review of the structures involved in manufacturing and breakdown

The organelles of the endomembrane system are interconnected structurally and functionally

Peroxisomes – are metabolic compartments that do not originate from the endomembrane system

Energy-Converting Organelles

4.13 Mitochondria harvest chemical energy for food

Mitochondria – (singular, mitochondrion), carry out cellular respiration

- converts chemical energy of foods (sugar) to the chemical energy of the molecule ATP - power house of the cell

*ATP (adenosine triphosphate) – main energy source for cellular work

4.14 Chloroplasts convert solar energy to chemical energy

Chloroplast – where photosynthesis takes place

Stroma – contains chloroplast DNA and ribosomes as well as many enzymes Thylakoid – network of interconnected sacs Granum – stacks of thylakoids

4.15 Mitochondria and chloroplasts evolved by endosymbiosis

Endosymbiont Theory – states that mitochondria and chloroplasts were formerly small prokaryotes

The Cytoskeleton and Cell Surfaces

4.16 The cell’s internal skeleton helps organize its structure and activities

Cytoskeleton – network of protein fibers

o Microfilaments – enable cells to change shape and moveo Intermediate filaments – reinforce the cell and anchor certain organelleso Microtubules – give the cell rigidity and act as track for organelle movement

4.17 Cilia and Flagella move when microtubules bend

4.19 The extracellular matrix of animal cells function in support and regulation

4.20 Three types of cell junction are found in animal tissues

Tight junction – bind cells to form leakproof sheets Anchoring junctions - rivet cells into strong tissues Gap junctions – allow substances to flow from cell to cell

4.21 Cell walls enclose and support plant cells

Chapter 5 : The Working Cell

Membrane Structure and Function

5.1 Membranes are fluid mosaics of lipids and proteins with many functions

Fluid Mosaic - Membranes are composed of a bilayer of phospholipids with embedded & attached proteins

5.2 Membranes form spontaneously, a critical step in the origin of life

5.3 Passive transport is diffusion across a membrane with no energy investment

Diffusion – spontaneous movement of a substance down its concentration gradient

Passive Transport – the diffusion of a substance across a biological membrane, with no expenditure in energy

5.4 Osmosis is the diffusion of water across a membrane

5.5 Water balance between cells and their surroundings is crucial to organisms

Tonicity – the ability of a surrounding solution to cause a cell to gain or lose water

Cells shrink in hypertonic solution, and swell in a hypotonic solution.

5.6 Transport proteins can facilitate diffusion across membranes

Facilitated diffusion – polar substances can move across a membrane with the help of specific transport proteins

5.7 Research on another membrane protein led to the discovery of aquaporins

Aquaporin – protein channel

5.8 Cells expend energy in the active transport of a solute

5.9 Exocytosis and endocytosis transport large molecules across membranes

Exocytosis – a vesicle may fuse with the membrane and expel its contents

Endocytosis – the membrane may fold inward, enclosing material from the outside

Energy and the Cell

5.10 Cells transform energy as they perform work

Energy – capacity to cause change or to perform work

Kinetic energy – energy of motion Potential energy – energy stored in the location or structure of matter

Chemical energy – available for release in a chemical reaction

Law of thermodynamics:

1. Law of energy conservation – energy can change form but cannot be created or destroyed2. Energy transformation increase disorder (entropy)

5.11 Chemical reaction either release or store energyExergonic reaction – release energyEndergonic reactions – require energy and yield products rich in potential eneryMetabolism – cell’s chemical reactions

5.12 ATP drives cellular work by coupling exergonic and endergonic reacions

ATP – Adenosine Triphosphate Phosphorylation – phosphate transfer3 main types of cellular work: chemical, mechanical, and transport work

How Enzyme Function

5.13 Enzymes speed up the cell’s chemical reactions by lowering energy barriers

Enzymes – are protein catalysts that decrease the activation energy (EA) needed to begin a reaction

5.14 A specific enzyme catalyzes each cellular reaction

5.15 Enzyme inhibitors can regulate enzyme activity in a cell

Inhibitor – a chemical that interferes with an enzyme’s activity

Competitive inhibitor – competes with the substrate for the active site

Noncompetitive inhibitor – alters and enzyme’s function by changing its shape

Feedback Inhibition – helps regulate metabolism

5.16 Many drugs, pesticides, and poisons are enzyme inhibitors

Chapter 6 : How Cells harvest Chemical Energy

C ellular Respiration: Aerobic Harvesting of Energy

6.1 Photosynthesis and cellular respiration provide energy for life

Energy comes from the sun.

In photosynthesis (takes place in chloroplasts), the energy of sunlight is used to rearrange the atoms of carbon dioxide (CO2) and water (H20) to produce glucose and oxygen (O2)

6 CO2 + 6 H2O -> C6H12O6 + 6 O2

In cellular respiration (takes place in mitochondria), O2 is consumed as glucose is broken down to CO2 and H2O; the cell capture the energy released in ATP

C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + Energy (ATP + heat)

6.2 Breathing supplies O2 for use in cellular respiration and removes CO2

Respiration - “breathing”, exchange of gases- Aerobic (oxygen-requiring) harvesting of energy from food molecules by cells

6.3 Cellular respiration banks energy in ATP moleculesC6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + Energy (ATP + heat)

6.4 The human body uses energy from ATP for all its activities

6.5 Cells tap energy from electrons “falling” from organic fuels to oxygenRedox Reaction – movement of electrons from one molecule to another Oxidation – the loss of electrons from one substanceReduction – the addition of electrons to another substance

NAD+ (nicotinamide adenine dinucleotide) - an important player in the process of oxidizing glucose- which accepts electrons and becomes reduced to NADH

NADH – passes electrons to an electron transport chain

Stages of Cellular RespirationStage 1 : Glycolysis – breaking glucose into two molecules of a 3-carbon compound called pyruvateStage 2 : Pyruvate oxidation and the Citric Acid Cycle (Kreb’s Cycle)Stage 3 : Oxidative Phosphorylation

6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvateGlycolysis = “splitting of sugar”Substrate-level phosphorylation – an enzyme transfers a phosphate group from a substrate molecule to ADP, forming ATP

6.8 Pyruvate is oxidized prior to the citric acid cycle

6.9 The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH2 molecules- a.k.a Kreb’s Cycle, in honor of Hans Kreb

6.10 Most ATP production occurs by oxidative phosphorylationIn mitochondria, electrons from NADH and FADH2 travel down the electron transport chain to O2, which picks up H+ to form water.

6.11 Interrupting cellular respiration can have both harmful and beneficial benefits

Poisons can block electron flow, movement of H+ through ATP synthase

6.12 Each molecule of glucose yields many molecules

Substrate-level phosphorylation and oxidative phosphorylation produce up to 32 ATP molecules for every glucose molecule oxidized in cellular respiration

Fermentation : Anaerobic harvesting of Energy

6.13 Fermentation enables cells to produce ATP without oxygen

Lactic acid fermentation – NAD+ is recycled from NADH as pyruvate is reduced to lactate Alcohol Fermentation – or in microbes, alcohol and CO2

6.14 Glycolysis evolved early in the history of life on Earth

Glycolysis - occurs in the cytoplasm of all organisms, evolved in ancient prokaryotes

Connections between Metabolic Pathways

6.15 Cells use many kinds of organic molecules as fuel for cellular respiration

Carbohydrates, fats, and proteins can all fuel cellular respiration

6.16 Food Molecules provide raw materials for biosynthesis

Chapter 7 – Photosynthesis: Using Light to Make Food

7.1 Autotrophs are the producers of the biosphere

Plants are

autotrophs (self-feeders), specifically photoautotrophs (uses light energy to make food)

Photosynthesis – plants convert CO2 and H2O to their own organic molecules and release O2 as a by-product

Photoautotrophs – producers of the biosphere

7.2 Photosynthesis occurs in chloroplasts in plant cells

Chlorophyll – green color, light absorbing pigment, solar energy to chemical energy

Mesophyll – green tissue in the interior of the leaf

Stomata – tiny pores

Chloroplast – surrounded by a double membrane

Stroma – thick fluid Thylakoids – a system of interconnected membranous sacs Grana – stacks of thylakoids

7.3 Scientists traced the process of photosynthesis using isotopes

Basic equation for photosynthesis:

6 CO2 + 6 H2O C6H2O6 + 6 O2

Isotopes – atoms with different number of neutrons

In the 1950s, scientists confirmed Van Niel’s hypothesis by using a heavy isotope of oxygen

7.4 Photosynthesis is a redox process, as is cellular respiration

In photosynthesis, H2O is oxidized and CO2 is reduced

Endergonic (absorbing energy in the form of work) – photosynthesis

7.5 Overview: The two stages of photosynthesis are linked by ATP & NADPH

Light reactions – convert light energy to chemical energy and release oxygen

Thylakoid membranes – light reaction occurs

NADP + - electron acceptor, reducing it to NADPH

NADPH – temporarily stores electrons and hydrogen ions and provides “reducing power” to the Calvin cycle

Calvin cycle – occurs in the stroma of the chloroplast

- sometimes referred to as the dark reactions or light-independent reactions

Carbon fixation – as CO2 entering the Calvin cycle

Photosynthesis (two stages) – Photo, Greek word “light”, synthesis, meaning “putting together” refers to the sugar construction of the Calvin cycle

For chloroplast to produce sugar from carbon dioxide in the dark, they would need to be supplied with ATP and NADPH.

The Light Reactions: Converting Solar Energy to Chemical Energy

7.6 Visible radiation absorbed by pigments drives the light reactions

Electromagnetic Spectrum – full range of electromagnetic wavelengths from the very short gamma rays to the very long wavelengths radio waves

Wavelength – distance between the crests of two adjacent waves

Photons – discrete packets of energy, has a fixed quantity of energy, the shorter the wavelength of light, the greater the energy of its photons

7.7 Photosystems capture solar energy

Photosystem – consist of a number of light-harvesting complexes surrounding reaction-center complex

Light-harvesting complex – contains various pigments molecules bound to proteins

7.8 Two photosystems connected by an electron transport chain generate ATP & NADPH

Tracing the light reactions, there is a flow of electrons from water to NADP + , which is reduced to NADPH, the source of electrons for sugar synthesis in the Calvin cycle.

7.9 Chemiosmosis powers ATP synthesis in the light reaction

Photophosphorylation – electron transport chain pumps H+ into the thylakoid space

The Calvin cycle uses the NADPH and ATP, occurs in the stroma

The Calvin Cycle: Reducing CO2 to Sugar

7.10 ATP and NADPH power sugar synthesis in the Calvin cycle

Steps of Calvin cycle: Carbon fixation, reduction, release of one molecule of G3P, and regeneration of RuBP

To synthesize one glucose molecule, the Calvin cycle uses 6 CO2, 18 ATP, and 12 NADPH.

7.11 Other methods of carbon fixation have evolved in hot, dry climates

C3 plants – first product of carbon fixation is the three-carbon compound 3-PGA, widely distributed (hot & dry – decrease crop yield)

Photorespiration – as O2 builds up in a leaf, rubisco adds O2 instead of CO2 to RuBP, a two carbon product of this reaction is then broken down in the cell

C4 plants – they first fix CO2 into a four carbon compound (hot & dry – stomata mostly closed, thus conserving water)

CAM plants – adapted to very dry climates (conserves water by opening its stomata and admitting CO2 only at night)

Photosynthesis Reviewed and Extended

7.12 Review: Photosynthesis uses light energy, carbon dioxide, and water to make organic molecules

Photosynthesis is the ultimate source of the food for almost all organisms and the oxygen they need for cellular respiration.

7.13 Photosynthesis may moderate global climate change

Greenhouse effect - sunlight warms Earth’s surface, which radiates heat to the atmosphere. CO2 and other greenhouse gases absorb and radiate some heat back to Earth.

7.14 Scientific study of Earth’s ozone layer has global significance

Solar radiation converts O2 high in the atmosphere to ozone (O3), which shields organisms from damaging UV radiation.