LIFE SCIENCE (copy)

Lesson 1: Cell Structures and Functions

·         All living things are made of cells, the basic unit of life.

·         Some organisms, like bacteria and protozoa, are unicellular – they consist of a single cell.

·         Other, like plants and animals, are multicellular, consisting of many different types of specialized cells.

·         Although cells differ widely in size and appearance, they all have basic structures in common. All cells have a cell membrane, a structure that keeps the cell’s contents separate from its external environment.

·         Inside the cell membrane is the cytoplasm, a watery, jellylike substance that can include other structures.

·         Finally, all cells have genetic material, which contains coded instructions for carrying out the cell’s activities.

·         In bacteria, the genetics material consists of a single molecule suspended in the cytoplasm. Bacteria are called prokaryotes.

·         In all other cells, the genetic material is contained within a nucleus.

·         Such cells are called eukaryotic cells. All plant and animals’ cells are eukaryotic.

·         A typical plant cell is shown below. Note that a plant cell has a cell wall, which gives the cell shape and rigidity, and an animal cell does not.

Lesson 2: Cell Processes and Energy

·         Green plants, some algae, and some bacteria use energy from sunlight to make food in a process called photosynthesis.

·         In photosynthesis, plants use sunlight to power chemical reactions that convert carbon dioxide gas and water into oxygen and the simple sugar glucose.

·         In the first stage of photosynthesis, light energy is captured by chloroplasts inside plant cells. Chloroplasts contain chlorophyll, a pigment that gives plants their green color. Chlorophyll absorbs light energy for photosynthesis.

·         As a results of photosynthesis, energy is stored in sugars and other carbohydrates

In the plants.

·         When energy is needed in a cell, carbohydrates are broken down to release the energy in a process called cellular respiration. In this process, oxygen from the air reacts with glucose from food to yield carbon dioxide, water, and energy.

Lesson 3: Human Body System

·         There are four levels of organization in the human body: (1) cells, the smallest unit of life; (2) tissues, groups of similar cells that perform a specific function, such as muscle tissue; (3) organs, groups of tissues that perform a function, such as the stomach; and (4) body systems, groups of organs working together to preform a function, such as digestion.

·         The circulatory system, sometimes called the cardiovascular system, consists of the heart and the blood vessels. Its main function is to move the blood, which transport substances like oxygen and nutrients, throughout the body.

·         The major organ of the body of the circulatory system is the heart, a muscle that contracts to pump blood.

·         Blood moves through the blood vessels from large arteries, to smaller arteries, to capillaries, to small veins, to large veins, and back to the heart.

·         The respiratory system consists of the nose, throat, trachea (windpipe), and lungs. Its function is to take oxygen from the air into the body when we inhale and to get rid of waste in the form of carbon dioxide when we exhale.

·         The trachea branches into two tubes called the bronchi, one of which goes into each lung. The bronchi branch into smaller tubes called bronchioles, each of which ends in an alveolus, a tiny spherical sac.

·         The digestive system consists of the mouth, esophagus, stomach, small intestine, and large intestine. Its function is to break down food into nutrients, which are used for cell processes including the production of energy, and to get rid of digestion wastes.

·         Digestion beings in the mouth, where the teeth grind food into smaller pieces, and saliva beings to break it down chemically.

·         Food is pushed by muscular action down through the esophagus into the stomach, where it is churned and further broken down by enzymes and stomach acids.

·         From the stomach it travels to the small intestine, where most of the nutrients are absorbed into the blood through tiny capillaries in the villi.

·         What remains goes to the large intestine, which removes water, leaving solid waste to be excreted through the rectum.

·         The nervous system consists of the brain, spinal cord, and nerves. Its function is to receive, process, and transmit information controlling body activities.

·         The brain has three main parts: the cerebrum, which controls functions such as thinking, seeing, and speaking; the cerebellum, which coordinates movement and position; and the brainstem, which controls breathing and heart rate.

Lesson 4: Health Issues

·         Health can be affected by infections, nutrition, and substance abuse. An infection is the invasion of the body by germs—microorganisms that cause disease. It is often characterized by fever and other symptoms. Germs can enter the body through breaks in the skin (for example, tetanus), with air (for example, influenza), in contaminated food and water (for example, food poisoning), by contact with contaminated blood and saliva (for example, rabies), or through sexual activity (for example, gonorrhea).

·         Infections can be grouped according to the type of microorganisms that cause them. The most common germs are bacteria and virus, although infections can be caused by fungi, protozoans, and worms.

·         The body has natural defenses against infection, such as the skin, the mucous membranes in the nose, tears, and acid in the stomach. If germs get past these defenses, the immune system produces antibodies that destroy the germs.

·         In developed nations, infectious diseases are less common than they used to be because of better nutrition and living conditions, safer water and sewage systems, immunization (which provides protection against specific infections diseases), and antibiotics drugs that fight bacteria.

·         Nutrients are substances that are needed for growth, normal functioning, and maintenance of cells. The body does not produce nutrients; instead we get them from the food we eat.

·         The nutrients that humans need for good health include proteins, carbohydrates (sugars and starches), fats, vitamins, minerals, and water.

·         Drugs are substance that affect the structure or function of the body. They are usually used to treat disease or relieve its symptoms, although some drugs, like nicotine in tobacco, have no medical purpose.

·         The nonmedical use of a drug to the point that it interferes with a person’s normal functioning is called drug abuse, or substance abuse.

·         Drug abuse can lead to addiction, to severe form of dependance that causes physical changes in the body so that when the drug wears off or is stopped, withdrawal symptoms such as nausea and pain occur. Heroin, speed, alcohol, nicotine, and barbiturates are frequently abused addictive drugs.

·         A milder form of dependance than addiction is psychological dependance, or habituation. In this type of dependance, the urge to take the drug is strong, even though there are no withdrawal symptoms.

·         Examples of drugs that can cause habituation in humans are marijuana and hallucinogens. People also abuse substances that are not drugs, like glue, gasoline, and aerosols. Most of these substances are inhalants—they are sniffed for their effect on the nervous system. Inhalants generally depress, or slow, the functioning of the nervous system, sometimes causing their users to lose control or become unconscious.

Lesson 5: Reproduction and Heredity

·         All species of organisms reproduce in some way. There are two types of reproduction.

·         In asexual reproduction, an individual organism produces offspring identical to the parent. For example, in a type of asexual reproduction called budding, a tiny freshwater animal called hydra grows buds that develop into offspring.

·         In sexual reproduction, two sex cells combine to form unique offspring with characteristics from both parent cells.

·         In humans and many other species, those specialized sex cells are called sperm and ova.

·         Physical characteristics of organisms are called traits.

·         The passing of traits from parents to offspring in sexual reproduction is called heredity.

·         The first person to study heredity in a systematic way was an Austrian monk, Gregor Mendel (1822-1884). He bred plants and observed that sometimes offspring plants.

·         Mendal experiment with purebred pea plants—plants that always produced offspring with the same form of a trait as the parent. For example, purebred short plants always produced short offspring. First he crossed purebred short plants with purebred tall plants. In the first generation of offspring, all the plants were tall—the shortness trait had vanished. When the first-generation offspring reproduced, about three-quarters of the next generation of plants were tall, and one-quarter were short. The shortness trait had reappeared.

·         Eventually he concluded that individual factors from each parent plant control the inheritance of specific traits. An offspring plant inherited on factor from the female parent and one from the male parent. Mendal concluded that one factor in a pair can hide the other factor. For example, the tallness factor hid the shortness factor in the first generation of offspring.

·         The factors that control traits are called genes.

·         Different forms of a gene are called alleles.

·         The gene that controls pea plant height, for example, has one allele for tallness and one allele for shortness. Each pea plant inherits one allele for the height gene from each parent. Therefore, any pea plant may have (1) two alleles for tallness, (2) two alleles for shortness, or (3) one allele for shortness and one for tallness. In the third case, the dominant allele, the tallness allele, controls the appearance of the trait. The recessive allele, the shortness allele, is hidden. For recessive trait to appear in an individual, the individual must inherit two recessive alleles.

·         All the offspring in the first generation were hybrid—each one had allele for tallness and one for shortness. Because the tallness allele is dominant, all he first generations plants were tall.

Lesson 6: Modern Genetics

·         Years after Mendel died, scientists identified chromosomes, rod-shaped structures in the nucleus of each cell, as responsible for carrying genes from parent organisms to their offspring.

·         One chromosome can contain thousands of genes on a single long molecule of deoxyribonucleic acid (DNA). A DNA molecule is shaped like a spiral ladder. The sides of the ladder are made of deoxyribose—a sugar—and phosphate. Each rung of the ladder is made of a pair nitrogen bases. There are for of these bases: adenine (A), guanine (G), thymine (T), and cytosine (C). the four bases pair up in a specific way: a always pairs with T, and C always pairs with G.

·         During protein synthesis, the information from a gene in the cell’s nucleus is used to produce a protein on ribosomes in the cytoplasm.

·         Messenger ribonucleic acid (RNA), transmits the code from the DNA.

·         Each set of three base pairs on the messenger RNA, called codon, contains instructions for creating an amino acid—a protein building block.

·         The sequence of codons determines that sequence of amino acids n the protein and thus the specific protein to be made. So, the order of bases on the gene forms a genetic code for the synthesis of a particular protein.

·         Genetic engineering has been used to produce medicines, such as insulin. It has been more controversial when used to improve foods. Finally, the entire human genome, or genetic code, has been decoded, making possible many advances in medicine.

Lesson 7: Evolution and Natural Selection

·          In 1831, the British ship the Beagle set sail with naturalist Charles Darwin (1809-1882) abroad. Darwin’s job was to observe living things he encountered. His observations during this five-year trip around the world led him to formulate an important scientific theory, the theory of evolution.

·         The sizes of the iguanas’ claws and the birds’ beaks are examples of adaptions traits that help on organisms survive in its organisms.

·         Darwin explained that species evolve because of natural selection. By this process, individuals that are better adapted to their environments are more likely to survive and reproduce, passing their favorable adaptations to their offspring.

·         Members of a species have different traits, called variations. Some variations make individuals better adapted to survive in their environment.

 Lesson 8: Organisms of Ecosystems

·         An ecosystem is an area consisting of a community of organisms—plants, animals, fungi, bacteria—and the physical environment in which they live—soil, air, water, and climate.

·         Earth as a whole is an enormous ecosystem called the biosphere.

·         Some of the organisms, such as green plants, are called producers because they use energy from the sun to make their own food through photosynthesis.

·         Other organisms, called consumers, depend on producers to meet their energy needs.

·         These organisms eat plants, or eat organisms that eat plants, to get energy. The complex pattern in which energy passes through an ecosystem is called a food web. A simple food web for a wooded area is shown here.