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The Big Picture: A Review of Biology
Chemistry of Life
Organic Compounds
 A compound is a combination of 2 or more atoms
 An organic compound is a compound that contains carbon atoms
 An inorganic compound is a compound with no combination of carbon atoms ex. Water
 Six most important elements essential to life: Carbon, Hydrogen, Nitrogen, Oxygen,
Phosphorus, Sulfur (CHNOPS)
The Four Types of Organic Compounds (The Molecules of Life) made from the 6 elements:
 Carbohydrates: Sugars used for short term energy – major source of energy
 Lipids: Fats and oils used for long term energy
 Proteins: Made up of amino acids; used for construction materials and chemical reactions in
the body
o Enzymes: Special types of proteins that speed up chemical reactions in the body but
are not changed by the reactions
 Nucleic acids: DNA genetic information, RNA – protein synthesis, ATP – energy for cells
Cell Biology
Cells
 A cell is the smallest unit that is alive and can carry on all the processes of life
 Cells make up organisms (living things)
o Unicellular organisms are made up of 1 cell
o Multicellular organisms are made up of many cells
 Cells contain organelles, which are specialized compartments that carry out a specific function
 Types of cells
o Eukaryotic cells contain a nucleus, such as animal and plant cells
o Prokaryotic cells contain no nucleus, such as bacteria
Animal Cells (Eukaryotic Cell)
 Usually round
 Organelles include
o nucleus: controls cell activities
o cell membrane: controls what enters and leaves the cell and also protects the cell
o endoplasmic reticulum (ER): passageway/tunnels for compounds and proteins to move
through the cell
o Golgi body: processes, stores and packages protein
o Ribosomes: make proteins
o Mitochondria: makes energy for the cell (powerhouse of the cell)
o Lysosome: contains enzymes that digest waste and old organelles
o Cytoplasm: fills the empty space of the cell
o Vacuole: stores food, water, and waste
o Centrioles: assists in cell division and is only found in animal, not plant, cells
Plant Cells (Eukaryotic Cell)
 Usually square
 Organelles include
o Everything that an animal cell has plus Chloroplasts, Cell Wall and Central Vacuole
o Chloroplast: Traps sunlight to make food for the plant
o Cell wall: Protects the cell
o Central Vacuole – large central storage for water, wastes and nutrients
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Bacterial cells (Prokaryotic Cell)
 Smaller and simpler than plant or animal cells
 Bacteria are unicellular
 No nucleus
 Have a single closed loop of DNA, cell wall, cell membrane, cytoplasm and ribosomes
 Some have a capsule (shell for protection), pili (short hair like structures to hold onto host
cells), and flagella (whip like structure for movement)
Cell membrane
 Made up of molecules called phospholipids
 Phospholipid bilayer is the 2 layers of phospholipids that make up the cell membrane
 Cell membrane is fluid, which means that it is constantly flowing and moving over the cell
 Cell membrane is selectively permeable, which means that it allows small compounds, but not
large ones, to pass right through
 There are different ways that materials are transported across the cell membrane
o Passive transport: requires no energy
 Diffusion: compounds move from high to low concentration
 Osmosis: diffusion of water
 Facilitated Diffusion: protein carriers, no energy (ATP) used
o Active transport: requires energy
 Endocytosis: large compound are brought into the cell
 Exocytosis: large compounds are exported out of the cell
 Types of solutions
o Hypotonic solutions cause water to move into the cell so the cell swells up
o Hypertonic solutions cause water to move out of the cell so the cell shrivels up
o Isotonic solutions cause no net movement of water into or out of the cell
Photosynthesis
 Process by which organisms use energy from sunlight to make their own food (glucose)
 Glucose is a simple sugar - monosaccharide
 Photosynthesis occurs in the chloroplasts of plant cells and some bacteria
 Chloroplasts have a green pigment called chlorophyll
 Steps of photosynthesis
o 1. Light reaction: chlorophyll in the chloroplasts absorbs sunlight
o 2. Dark reaction: The energy from the sunlight is used to make glucose
 Light energy is completely changed into chemical energy (glucose)
 Chemical equation for photosynthesis
6CO2 + 6H2O + light energy  C6H12O6 + O2
carbon dioxide water in the presence of chlorophyll
glucose
oxygen
Cellular Respiration
 Process that breaks down glucose in order to make energy for an organism
 ATP: compound that stores energy in an organism
 Occurs in the mitochondria of the cell
 Two types of cellular respiration
o Aerobic respiration: requires oxygen to occur
 Mostly happens in animals and plants
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There are 3 steps in aerobic respiration
 Step 1 is glycolysis: glucose is cut in half
 Step 2 - citric acid cycle: glucose halves
 Step 3 electron transport chain: electrons combine with oxygen and are
used to make ATP
Chemical equation for cellular respiration
C6H12O6 + O2  6CO2 + 6H2O + ATP energy
glucose
oxygen
carbon dioxide
water
ATP energy
 Aerobic respiration is the opposite reaction of photosynthesis
o Anaerobic respiration: does not require oxygen to occur
 Mostly happens in bacteria and yeast
 Also called fermentation –
 Two types: Alcoholic fermentation and Lactic Acid fermentation
 Makes less ATP than aerobic respiration
Chromosomes
 DNA strands located on chromosomes in the nucleus which stores hereditary information
 Made up of genes, which are traits of an organism
 Cells will die if their DNA is damaged or removed
 Humans have mostly diploid cells, 2 of each type of chromosome (two sets)
o Homologous chromosomes are 2 of the same type of chromosome
o We have 23 types of chromosomes
o We have 46 chromosomes total
23 chromosomes from mom + 23 chromosomes from dad
 Human gametes (sperm and egg cells) are haploid cells, which means that they have 1 of each
type of chromosome
o Sperm and egg cells have 23 chromosomes
 Autosomes: Chromosomes that do not determine gender
 Sex chromosomes: Chromosomes that determine gender (the 23rd chromosome)
o Girls are XX, Boys are XY
 Karyotype: ordered picture of an organism’s chromosomes
o Healthy individuals have 2 of each type of chromosome
o Individuals with Down Syndrome have three #21 chromosomes
Cell Cycle
 The cell cycle is the phases in the life of a cell
 Interphase
o G1 phase: Cell grows
o S phase: DNA synthesis (chromosomes are copied) (DNA Replication)
o G2 phase: Cell grows
 Mitosis phase: Mitosis (nuclear division) occurs
o Prophase
o Metaphase
o Anaphase
o Telophase
 Cytokinesis: cytoplasm divides - two new identical cells are formed
 Chromosomes must be copied before mitosis can occur so that new cells receive the same
chromosomes found in the old cells
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Mitosis
 Division of a cell into 2 genetically identical cells
 Before mitosis: Chromosomes have copied themselves during the S Phase
 Sister chromatids: original chromosome and its exact copy are attached to each other
 Phases of mitosis
o 1. Prophase: Nuclear membrane falls apart and spindle fibers start to form
o 2. Metaphase: Sister chromatids line up along the middle of the spindle fibers
o 3. Anaphase: Sister chromatids separate and move to opposite ends of the cell
o 4. Telophase: Spindle fibers break down and new nuclear membrane forms around each
set of chromosomes
 Cytokinesis occurs when the cytoplasm actually divides, forming two new cells
Genetics
Meiosis
 Type of cell division that produces gametes (sex cells), such as sperm and egg cells
 Fertilization: Process of an egg and a sperm cell combining to produce a zygote
o Zygote: Offspring that is only 1 cell big – produced by the fusion of egg and sperm
o Egg cell (23 chromosomes) + sperm cell (23 chromosomes) = offspring (46 chromosomes)
 Steps in meiosis
o 1. Before meiosis:
 2 chromosomes of the same type come together to make a chromosome pair
 Each chromosome doubles
 This gives 4 chromosomes stuck together
o 2. Meiosis I: Chromosome pairs cross over, exchange genetic material, separate into two
new cells
o 3. Meiosis II: Each chromosome separates from its copy into 4 new genetically different
haploid cells (half the number of chromosomes)
 Meiosis, one cell becomes four genetically different haploid cells called gametes (sex cells)
 Mitosis, one cell becomes two cells, genetically identical diploid cells (somatic cells)
DNA
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Deoxyribonucleic acid
Makes up the chromosomes in the nucleus and never leaves the nucleus
A chromosome is a chain of different genes
DNA has a double helix shape made up of nucleotides held together by a Hydrogen bond
DNA nucleotides – Sugar – deoxyribose, Phosphate group, Nitrogen bases – A,T, C, G
Nitrogen bases: Purines: adenine (A), guanine (G), Pyrimidines: thymine (T), cytosine (C)
Base Pairing Rule – Nitrogen bases - A binds T and G binds C (Scientist – Chargaff)
DNA is complementary, which means that the bases on one strand match up to the bases on
the other strand
o For example: Strand 1: ATG CCT GAC
Strand 2: TAC GGA CTG
DNA replication is the process by which DNA copies itself and each new piece of DNA is
made up of 1 old strand and 1 new strand using enzymes, helicase (unwinds DNA strand) and
DNA polymerase (adds nucleotides to each DNA strand).
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RNA
 Ribonucleic acid
 RNA is a copy of DNA that goes out into the cytoplasm
 RNA is single stranded, contains the sugar, ribose and has uracil (U) rather than thymine (T)
o U binds A
and
G binds C
o If the DNA segment is
ATG CCA AAG
Then the RNA will be
UAC GGU UUC
Using DNA to make protein
 1. Transcription: DNA in the nucleus is used as a template to make messenger RNA (mRNA)
o DNA has all the directions the cell needs to live, mRNA transcribes the information
 2. mRNA moves out into the cytoplasm to the ribosomes
 3. Translation: The mRNA attaches to a ribosome and tRNA and directs the production of a
protein using a codon, a three nucleotide base sequence that codes for an amino acid.
o tRNA translates with an anticodon and attaches an amino acid.
o A polypeptide chain of amino acids form a proteins which do all the work in the cell
Mutations
 A mutation is a change in a gene or chromosome
 If the mutation happens in a body cell, it only affects the organism that carries it
 If the mutation happens in a sex cell, it can be passed on to offspring
 Mutations can be
o harmful if they reduce an organism’s chances for reproduction or survival
o helpful if they improve an organism’s chances for survival
o neutral if they do not produce an obvious changes in an organism (silent mutation)
o lethal if they result in the immediate death of an organism
 Mutations can occur spontaneously or be caused by a mutagen, which is a factor in the
environment like UV and chemicals.
Mendelian Genetics
 Gregor Mendel, an Austrian monk, Father of Modern Genetics
 Genetics is the study of heredity, passing of traits from one generation to the offspring
 Humans have 2 genes for every trait
o Alleles: different forms of a single trait, like blue and brown are two eye color alleles
 Dominant gene: “Stronger” of 2 genes and shows up in the organism
o Represented by a capital letter
o B is the dominant gene for brown eyes
 Recessive gene: “Weaker” of 2 genes and only shows up when there is no dominant gene
present
o Represented by a lowercase letter
o b is the recessive gene for blue eyes
 Homozygous (purebred): When 2 genes are alike for a trait
o BB is homozygous for brown eyes, bb is homozygous for blue eyes
 Heterozygous (hybrid): When 2 genes are different for a trait
o Bb is heterozygous
 Mendel’s Law of Segregation states that the 2 genes we have for each trait are separated from
one another when gametes, egg and sperm cells, are formed.
 Mendel’s Law of Independent Assortment states that the gene for one trait is inherited
independently of the genes for other traits
o Only true when the genes are on different chromosomes
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Punnett Squares
 Punnett Squares are charts that are used to show the possible gene combinations in a cross
between 2 organisms, showing probability
 If B is the dominant gene for brown eyes and b is the recessive gene for blue eyes*
 Genotype: The genes of an organism (Bb); the type of gene
 Phenotype: The physical appearance of an organism (Brown eyes); physical traits
Parents
Bb x bb
B
Bb
b
bb
b
b
Bb
Parents
Bb x Bb
Offspring genotype
50% Bb
50% bb
bb
Offspring phenotype
50% Brown eyes
50% Blue eyes
B
b
BB
Bb
Bb
bb
B
b
Bb
Offspring genotype
25% BB
50% Bb
25% bb
Offspring phenotype
75% Brown eyes
25% Blue eyes
Human Genetics
 Multiple alleles are three or more alleles that exist for a single gene
o For example, A, B, and O are the multiple alleles for blood type
o The possible blood types are A, B, AB, and O
 You can be A+ or A-, B+ or B-, AB+ or AB-, O+ or O- depending on whether your
blood cells have a special Rh protein
 Codominance occurs when 2 dominant genes are expressed and both genes are seen in the
organism
o AB blood is codominant, a cat with black and white spots is codominant
 Incomplete dominance occurs when 2 dominant genes are expressed and blended together in
the organism
o If the red flower color gene (R) is mixed with the white flower color gene (W) then the
offspring will be pink (RW)
 A polygenic trait is a trait that is controlled by more than one pair of genes, like skin color
 A sex-linked trait is a trait that is found on the X chromosome, such as colorblindness,
hemophilia and male pattern baldness
o Females are XX so have 2 copies of sex-linked traits
o Males are XY so have 1 copy of sex-linked traits
Ecology
Ecology
 Ecology is the study of the interactions of organisms with one another and their environment
 A community is a group of various species that live in the same habitat and interact
 A habitat is the physical location of a community
 An ecosystem is a community of organisms and their abiotic environment
 The diversity of an ecosystem is a measure of the number of species living in the habitat
 There are different feeding groups of organisms
o Autotrophs: organisms that make their own food, plants and some bacteria
o Heterotrophs: organisms that obtain food by eating other organisms:
 Herbivores: eats only plants
 Carnivores: eats meat
 Omnivores: eat plants and meat
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There are different factors is an ecosystem
o Abiotic factors are nonliving things and environmental factors:
 Weather, climate, temperature and water.
o Biotic factors are living things:
 Food, predators, disease, and parasites.
 Producers: organisms that take in energy and make their own food
 Consumers: organisms that eat other organisms for energy
 Decomposers: organisms that eats waste products and dead organisms for energy
There are different Trophic Levels in a food chain
o A trophic level is a feeding level in an ecosystem
o A food chain is a pathway of energy transfer through feeding patterns of organisms
o 1st trophic level is a producer
o 2nd trophic level is a primary consumer
o 3rd trophic level is a secondary consumer
o 4th trophic level is a tertiary consumer
o Last trophic level is a decomposer
Every time an organism eats, it obtains energy from its food
o So energy is transferred from the 1st to the 2nd to the 3rd trophic level and so on (but some
of this energy does get lost along the way as heat)
o Energy pyramid: triangular diagram that shows how much energy is transferred to the
different trophic levels through the ecosystem’s food chain
o 10% Rule: organisms store only 10% of the consumed energy. 90% is lost as heat.
A food web is a network of connected food chains in an ecosystem
Cycles of Matter
 Water, Nitrogen, Carbon, Hydrogen, Phosphorus, and Oxygen are recycled in the environment
 The Nitrogen Cycle
o Nitrogen in the atmosphere is taken in by bacteria that live in plant roots
o The nitrogen is passed onto the plants and any animals that eat the plants
o Once the plant or animal has died, decomposers (bacteria) again take up the nitrogen in the
dead material and send it back to the atmosphere
 The Water Cycle
o Precipitation, such as rain and snow, fall to the earth
o The water either
 seeps into the ground for plants to use and the plants give off excess water back to the
atmosphere
 or runs off the land to lower-lying bodies of water where it evaporates back into the
atmosphere
 The Oxygen-Carbon Cycle
o Carbon dioxide from the atmosphere is taken in by plants who use it during photosynthesis
and release oxygen back into the atmosphere
o Oxygen in the atmosphere is taken in by animals and plants who use it during respiration
and release carbon dioxide back into the atmosphere
 The Phosphorus Cycle
o Important part of ATP and DNA
o Phosphorus is found in soil and rocks as calcium phosphate and dissolves in water
o When organisms die and decompose, the phosphorus is returned to the soil
o Roots of plants absorb phosphate; animals eat plants and reuse the organic phosphorus
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Interaction in an environment
 Each organism has a niche, or role, to play in its environment
 Competition is a struggle between organisms for resources, such as food, water, shelter
 Predators are organisms that catch, kill, and eat other organisms called prey
 Symbiosis is a close relationship between 2 organisms in which one organism lives near, on,
or even inside another organisms and in which at least one organism benefits
o There are three types of Symbiosis
o 1. Commensalism is when one of the 2 organisms benefits from the symbiosis
o 2. Mutualism is when both organisms benefit from the symbiosis
o 3. Parasitism is when one organism benefits (parasite) and the other organism is harmed
(host) from the symbiosis
 The parasite feeds on the host while it is still alive, weakening but not killing it
 An adaptation is a change in the behavior or physical characteristics of a species that make it
better suited to its environment
 Populations of organisms increase and decrease due to overpopulation of a competitor or
predator, disease, lack of food or water or shelter, and extreme weather
 Ecosystems are constantly changing due to changing populations of organisms, changing
weather, natural disasters, and human activity
 Every time a change occurs, the balance of the ecosystem has to be readjusted
The Theory of Evolution
Evolution
 Evolution is a change in a species over time
 The theory of evolution was stated by Charles Darwin and is based on natural selection
 Natural selection states that organisms with traits well suited to an environment are more
likely to survive and produce more offspring than organisms without these favorable traits
 Biodiversity: variety of organisms in a given area, a variety species in a community, or the
variety of communities in an ecosystem: genetic variation within a population
 The Theory of Evolution is supported by evidence that includes
o Adaptation: traits (structures and behaviors) that organisms have that improve survival and
reproduction
o The Fossil Record: traces or remains of organisms that lived in the past
o Comparative Anatomy: the bodies of different organisms are compared to see if they are
related
 Homologous structures are body structures on different organisms that are similar
 Vestigial structures are body structures that may have served a purpose in ancient
ancestors but no longer are functional in current organisms
o Developmental Biology: The fact that all vertebrate embryos look very similar as they
develop before birth
o Biochemistry: The fact that the DNA of closely related organisms looks very similar
o Biogeography: study of the location of organisms around the world.
Taxonomy
 Taxonomy is the science of classification
 Organisms are organized into 7 different levels of taxonomy (King Philip Came Over For
Good Snacks)
o 1. Kingdom – most broad
o 5. Family
o 2. Phylum
o 6. Genus
o 3. Class
o 7. Species – most specific
o 4. Order
 Closely related organisms have more levels of taxonomy in common than unrelated organisms
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There are six kingdoms of living things (Archie Eats Pretty Fantastic Apple Pies)
o 1. Archaebacteria: bacteria that live
o 4. Fungi: Mushrooms, yeasts,
in extreme environments
molds
o 2. Eubacteria: common bacteria
o 5. Animalia: animals
o 3. Protista: Single-celled organisms
o 6. Plantae: plants
Every organism has a unique two-word scientific name- binomial nomenclature
o The first word is the genus, the second word is the species (Humans are Homo sapiens)
Some scientists prefer to organize organisms into domains rather than kingdoms
o There are three domains (Archie Eats Eels)
o 1. Archaea: Bacteria that live in extreme environments
o 2. Eubacteria: Common bacteria
o 3. Eukarya: Organisms whose DNA is in a nucleus (Eukaryotes)
Anatomy and Physiology
The Human Body Systems
Body Organization
 Embryonic stem cells can become more than one type of cell.
 Cells, tissues, organs, organ systems.
 The human body contains four types of tissues:
o Epithelial Tissue – covering of organs
o Nervous Tissue – made of neurons, nerve cells.
o Connective Tissue – bones, blood, ligaments, tendons
o Muscle Tissue –
o Smooth muscle – found in intestines and bladder,
o Cardiac muscle – found only in the heart
o Skeletal muscle- muscle connected to bones
 Tissues that work together form organs.
 Organs that work together form organ systems.
 The body maintains homeostasis, a steady internal environment.
The Skeletal System
 The five important functions of the skeletal system are support, protection, movement, mineral
storage, and blood cell formation.
 The structure of a typical bone includes the periosteum, compact bone, spongy bone, and bone
marrow.
 Movable joints are made up of bone, cartilage, and ligaments.
o Saddle joint- thumb
o Pivot joint – neck
o Ball and Socket joint- hip
o Hinge joint- knee
o Gliding joint - foot
The Muscular System
 The human body contains skeletal, smooth, and cardiac muscle.
 Muscles switch between two processes to produce ATP.
 Skeletal muscle is made of muscle fibers, myofibrils, and sarcomeres.
 Actin filaments sliding inward along myosin filaments cause muscle contraction.
 Exercise affects strength, speed, endurance, fatigue, injury, and atrophy in muscles.
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The Integumentary System
 The structure of skin includes the epidermis, dermis, and subcutaneous layer.
 The skin protects the body and helps regulate body temperature.
 Hair and nails are made by cells in the skin.
 Melanin - dark pigment
 Keratin – protein that protects the skin, gives it texture and makes it waterproof.
 Skin disorders can be genetic, caused by infections, or the result of changes in the body.
The Cardiovascular System
 The cardiovascular system carries nutrients, oxygen, hormones, and wastes throughout the
body and distributes heat to maintain homeostasis.
 The structure of the heart chambers is related to their function.
o The atria are thin walled because they pump blood just to the ventricles.
o The ventricles are thick walled because they pump blood to either the lungs or the rest
of the body.
 The structure of blood vessels relates to their function.
o Arteries have thick, muscular walls to withstand the force of the pumped blood.
o Capillaries have thin walls to allow the exchange of gases and nutrients.
o Veins have valves that stop blood from flowing backward.
 The key components of human blood are
o plasma,
o red blood cells,
o white blood cells, and
o platelets.
 The lymphatic system works with the cardiovascular system by collecting fluids that leak out
of capillaries and returning those fluids to the cardiovascular system.
Cardiovascular Health
 The four main cardiovascular diseases are high blood pressure, arteriosclerosis, heart attack,
and stroke.
 The most important ways to prevent cardiovascular disease are to maintain a healthy diet,
exercise regularly, and avoid tobacco and alcohol use.
The Respiratory System
 Air enters the nasal passages, and then flows through the pharynx, the larynx, the trachea, the
bronchial tubes, and finally the bronchioles into the alveoli of the lungs.
 When the diaphragm and rib muscles contract, the chest cavity expands and air rushes in.
When these muscles relax, the chest cavity returns to a resting position and air rushes out.
 Oxygen is transported bound to hemoglobin (protein) inside red blood cells
 Most carbon dioxide is transported as bicarbonate ions in the plasma.
 Six common diseases of the respiratory system are asthma, bronchitis, pneumonia,
tuberculosis, emphysema, and lung cancer.
Nutrition
 Your body needs energy to breathe, pump blood, and grow. The more active you are, the more
Calories you burn to release energy.
 Carbohydrates, Proteins, and Fats provide most of the energy and building materials for the
body.
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Water, vitamins and minerals contribute to many functions, such as regulating chemical
reactions that release energy.
Good nutrition must be balanced with regular physical activity to maintain a healthy body.
Digestion
 The digestive system takes in food, breaks it down, both chemically and mechanically, into
molecules that the body can use, and gets rid of undigested molecules and waste.
 The mouth, esophagus, and stomach begin the process of digestion by breaking food into
small molecules.
 Enzymes enable chemical digestion of nutrients:
o Pepsin – along with Hydrochloric Acid - Stomach – Proteins into amino acids
o Amylase – Saliva and Pancreas – Starches into disaccharides
o Lipases – Pancreas – Fats into fatty acids and glycerol
o Bile – Liver and Gall Bladder – Fats into fat globules
 Absorption of nutrients takes place in the small intestine primarily, aided by secretions from
the liver and pancreas. Villi and microvilli absorb nutrients in small intestine.
o No food passes through the liver and the pancreas.
 Components of food that are not digested leave the body as wastes.
 No digestion takes place in the large intestines, but excess water and mineral ions are
absorbed through its wall.
Excretion
 By removing toxic chemicals, excretion enables the body to maintain its osmotic (water
concentration) and pH balance.
 Excretory Organs:
o Skin – excretes water, salts and nitrogen wastes.
o Lungs – carbon dioxide
o Kidneys – filter wastes out of the blood such as urea
 Nephron – the functional unit of the kidneys – each kidney has about one million nephrons.
 The kidneys filter wastes out of the blood and balance levels of molecules.
 Metabolic wastes are removed from the body through the formation and excretion of urine.
 Kidneys are vital to maintaining homeostasis, so damage to kidneys may eventually become
life-threatening.
Immune System –
Protecting Against Disease
 Skin and mucous membranes form strong barriers that prevent pathogens from entering the
body.
 When pathogens break through the body’s physical barriers, the body quickly responds with
second-line defenses—fever, inflammation, and the activation of special proteins that kill or
inhibit pathogens.
 When a pathogen infects a cell, the body produces immune cells that specialize in detecting
and destroying that specific pathogen.
Eliminating Invaders
 A specialized white blood cell called a helper T cells activates the specific immune response.
These cells coordinate two responses; the destruction of cells that have been infected by a
pathogen, and the removal of pathogens at large in the body.
 Cytotoxic T cells attack and kill cells that have been infected by pathogens.
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The B cell response removes extracellular pathogens from the body and prevents further
infection.
After an immune response, memory cells continue to protect the body from previously
encountered pathogens.
Immune System Dysfunctions
 An allergic reaction is an excessive immune response to a normally harmless antigen.
 In an autoimmune disease, the body launches an immune response so that body cells are
attacked as if they were pathogens.
 When the immune system does not function, the body is unable to fight and survive infections
by pathogens that do not cause problems for a robust immune system.
Structures of the Nervous System
 The central nervous system responds to internal and external information.
o Central Nervous System – the brain and the spinal chord.
 The Peripheral Nervous System contains sensory and motor neurons that carry information
between the central nervous system and the rest of the body.
o Peripheral Nervous System branches throughout the body.
 A spinal reflex is an involuntary movement triggered by sensory input and produced by neural
circuitry limited to the spinal cord.
Neurons and Nerve Impulses
 Electrical signals in the nervous system are caused by the movement of ions across the cell
membrane of neurons.
 Neurons are nerve cells consisting of
o Dendrites – act as antennae to receive information
o Axons – long projection of nerve cell that conducts electric impulses
o Axon Terminals – the end of the axons – how neurons communicate with other cells
o Myelin Sheath – insulation layer of axons
o Nodes of Ranvier – gaps between myelin sheaths that conduct nerve impulses.
 A neuron’s dendrites gather information from other cells, the cell body integrates this
information, and the axon sends the information to other cells.
 All nerve impulses begin when the resting state of a neuron is changed by a signal from
another neuron or from the environment.
 Neurons communicate with other cells at specialized junctions called synapses.
 Chemicals are released at synapses.
Sensory Systems
 Specialized neurons called sensory receptors detect sensory stimuli and convert them to
electrical signals. These signals then can be interpreted by the brain.
 The major classes of sensory receptors are photoreceptors, mechanoreceptors,
chemoreceptors, pain receptors, and thermoreceptors.
 Specialized regions of the cortex detect different sensory information.
Nervous System Dysfunction
 Many psychoactive drugs produce physiological dependence and addiction when abused.
 Addiction occurs when repeated use of a drug alters the normal functioning of neurons and
synapses.
 Damage to the nervous system can occur as a result of disease, traumatic injury, or exposure
to chemicals.
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Hormones
 The endocrine system regulates metabolism; salt, water, and nutrient balance in the blood;
controls the body’s response to stress; and regulates growth, development, and reproduction.
 Endocrine glands and endocrine tissues produce and release hormones.
 Hormones can affect only cells that have receptor proteins that match the hormone.
 Amino acid–based hormones bind to the surface of target cells and cause changes by a second
messenger system. Steroid hormones enter target cells and cause changes by direct gene
activation.
 The body uses negative feedback, positive feedback, and antagonistic hormones to regulate
the levels of hormones and their products.
Major Endocrine Glands
 The hypothalamus and the pituitary gland work together to control the functions of the
endocrine system.
 The thyroid gland, parathyroid gland, pancreas, and pineal glands regulate metabolism.
 The adrenal medulla regulates short-term responses to stress. The adrenal cortex regulates
long-term responses to stress.
 Reproduction is regulated by gonadotropins, which are released by the pituitary gland, and by
sex hormones, which are released by the gonads.
The Male Reproductive System
 The male reproductive system has two testes that produce sperm and testosterone.
 The vas deferens carries sperm into the urethra. Sperm leave the body by passing through the
urethra.
 As sperm cells move into the urethra, they mix with fluids secreted by three exocrine glands:
the seminal vesicles, the prostate gland, and the bulbourethral glands.
 After the semen is deposited in the female reproductive system, sperm swim until they
encounter an egg cell or until they die.
The Female Reproductive System
 The ovaries produce egg cells. Ovaries also secrete estrogen and progesterone.
 During the reproductive years, the female body undergoes a hormonal cycle that causes
periodic changes. These changes prepare the body in the event that an egg is fertilized.
 If pregnancy does not occur, levels of estrogen and progesterone fall. The decrease in these
two hormones causes the lining of the uterus to be shed during menstruation.
Human Development
 When a sperm cell encounters an ovum, the sperm cell releases enzymes that break down the
outer layers of the ovum. The head of the sperm enters the ovum, and the nuclei of the ovum
and sperm fuse. This process, from encounter to fusion, is called fertilization.
 All of the embryo’s organ systems, as well as the supportive membranes that feed and protect
the embryo, develop during the first trimester of pregnancy.
 By the end of the third trimester, a fetus is able to live outside the mother’s body. A baby
leaves the mother’s body after labor.
Sexually Transmitted Infections
 Abstinence is the only sure way to protect yourself from contracting an STI.
 Common STIs include genital herpes, genital HPV, trichomoniasis, HIV/AIDS, hepatitis B,
chlamydia, and gonorrhea.