• cell differentiation

• stem cell

• tissue

• organ

• organ system

Levels of Organization

• All cells in a multicellular organism come from one cell: a fertilized egg.

• The process by which cells become different types of cells is called cell differentiation.

Multicellular Organisms (cont.)

Multicellular Organisms (cont.)

Stem cells are unspecialized animal cells that are able to develop into many different cell types.

Multicellular Organisms (cont.)

• Plants have unspecialized cells similar to animal stem cells.

• These cells are grouped in areas of a plant called meristems.

Tissues are groups of similar types of cells in multicellular organisms that work together to carry out specific tasks.

Multicellular Organisms (cont.)

• Humans, like most other animals, have four main types of tissue: muscle, connective, nervous, and epithelial.

• The three main types of plant tissue are dermal, vascular, and ground tissue.

Multicellular Organisms (cont.)

Multicellular Organisms (cont.)

• Organs are groups of different tissues working together to perform a particular job.

• Organ systems are groups of different organs that work together to complete a series of tasks.

Multicellular organisms usually have many organ systems that work together to carry out all the jobs needed for the survival of the organism.

Multicellular Organisms (cont.)

• organ system

• homeostasis

• nutrient

• Calorie

Transport and Defense

• lymphocyte

• immunity

• Groups of organs that work together and perform a specific task are organ systems.

• Organ systems provide movement, transport substances, and perform many other functions.

The Body’s Organization

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• The human body breaks down food through the process of digestion.

• Substances that are not used by the body are removed through the digestive system and by the excretory system.

Digestion and Excretion

The esophagus connects the mouth to the stomach—a flexible baglike organ that contains enzymes that break down food into smaller parts to be used by the body.

Digestion (cont.)

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• The small intestine has two functions—digestion and absorption.

• Nutrients are absorbed by the body through the small intestine.

Digestion (cont.)

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The liver makes bile and the pancreas makes enzymes, both of which break down food in the small intestine.

Digestion (cont.)

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• The large intestine receives solid waste from the small intestine.

• The large intestine absorbs excess water from the waste material.

• The rectum of the large intestine stores the solid waste until the waste is expelled from the body.

Digestion (cont.)

Some foods, like insoluble fiber, that are not digested leave the body through the rectum.

Digestion (cont.)

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• Nutrients are the parts of food used by the body to grow and survive.

• Proteins, fats, carbohydrates, vitamins, and minerals are all nutrients.

• Calories are a measure of the amount of energy in food.

Digestion (cont.)

The excretory system removes liquid and gas wastes from the body. This system includes—

Excretion

• lungs

• skin

• liver

• kidneys

• ureter

• bladder

• urethra

• When the liver breaks down proteins, urea forms. Urea is toxic if it stays in the body.

• The kidneys remove urea from the body by making urine.

Excretion (cont.)

• Urine leaves each kidney through the ureter and is stored in a flexible sac, called the bladder.

• Urine is removed from the body through the urethra.

Excretion (cont.)

The respiratory system exchanges gases between the body and the environment.

Respiration

• When you inhale, air enters the nostrils and passes through the pharynx to the trachea.

• Inhaling and exhaling require the movement of a muscle under the lungs called the diaphragm.

Respiration (cont.)

The trachea, or windpipe, connects the pharynx to the bronchi.

Respiration (cont.)

There are two bronchi; one enters the left lung and one enters the right lung.

Respiration (cont.)

The bronchi divide into smaller tubes that end in tiny groups of cells called alveoli.

Respiration (cont.)

The alveoli are surrounded by blood vessels called capillaries.

Respiration (cont.)

Respiration (cont.)

Gas Exchange

• Oxygen in the alveoli enters the capillaries.

• The blood inside capillaries transports oxygen to the rest of the body.

Circulation

The heart, blood, and blood vessels make up the circulatory system which transports nutrients, gases, wastes, and other substances through the body.

Circulation (cont.)

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• Blood vessels transport blood to all organs of the body.

• Contractions of the heart’s muscles pump blood to the rest of the body.

• Blood travels through the body in tiny tubes called vessels.

Circulation (cont.)

• Arteries carry blood away from your heart.

• Veins carry blood back to your heart.

Circulation (cont.)

Capillaries are tiny vessels that allow gases and nutrients to move between the blood and the entire body.

Circulation (cont.)

• The liquid part of blood is called plasma and contains nutrients, water, and CO2.

• Blood also contains red blood cells, which carry oxygen, and platelets, which help the body heal when a vessel is cut.

• White blood cells help the body defend itself from toxins and diseases.

Circulation (cont.)

Different people have different proteins on the surfaces of their red blood cells which scientists classify into groups called blood types.

Tonsils, the spleen, the thymus, bone marrow, and lymph nodes are parts of the lymphatic system.

Lymphatic System

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• The lymphatic system’s three main functions are removing excess fluids around organs, producing white blood cells, and absorbing and transporting fats.

• The lymphatic system helps your body maintain fluid homeostasis.

Lymphatic System (cont.)

• Fluid that travels through the lymph vessels flows into organs called lymph nodes, which protect the body by removing toxins, wastes, and other harmful substances.

• The lymphatic system makes white blood cells to help the body defend against infection.

Lymphatic System (cont.)

• Protection from infection or toxins is called immunity.

• The skeletal system produces immune cells, which include lymphocytes and other white blood cells, and the circulatory system transports them throughout the body.

• The immune cells attack and destroy viruses, bacteria, and other foreign substances.

Immunity

• Humans make billions of different types of antibodies.

• Infectious diseases are caused by pathogens, such as bacteria and viruses, and are usually contagious.

• A noninfectious disease is caused by the environment or a genetic disorder.

Immunity (cont.)

Immunity (cont.)

• The body’s first line of defense against viruses, bacteria, and harmful substances is the skin and mucus which prevent toxins and other substances from entering the body.

• The second line of defense is the immune response in which white blood cells attack and destroy harmful substances.

Immunity (cont.)

The third line of defense is immune cells which make antibodies that destroy harmful substances.

Immunity (cont.)

• compact bone

• spongy bone

• neuron

Structure, Movement, and Control

• reflex

• hormone

• The skeletal system protects internal organs, provides support, helps the body move, and stores minerals, such as calcium.

• An adult’s skeleton has 206 bones.

• The skeleton also contains ligaments, tendons, and cartilage.

Structure and Movement

• Compact bone is the hard outer layer of bone.

• Spongy bone is the interior region of bone that contains many tiny holes.

Structure and Movement (cont.)

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• The muscular system is made of three different types of muscle tissue.

• Skeletal muscle works with the skeletal system and helps you move.

Structure and Movement (cont.)

• Cardiac muscle is only in the heart.

• It continually contracts and relaxes and moves blood throughout your body.

Structure and Movement (cont.)

• Smooth muscle tissue is in organs such as the stomach and the bladder.

• Blood vessels also have smooth muscle tissue.

Structure and Movement (cont.)

• The brain and the spinal cord form the central nervous system.

• All other nerves are part of the peripheral nervous system that extends throughout the entire body.

Control and CoordinationD

oug Pensinger/G

etty Images

The nervous system is a group of organs and specialized cells that detect, process, and respond to information.

Control and Coordination (cont.)

Nerve cells, or neurons, are the basic unit of the nervous system.

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• Information enters the nervous system through neurons in the peripheral nervous system.

• Most of the information then is sent to the central nervous system for processing.

• After the central nervous system processes information, it signals the peripheral nervous system to respond.

Control and Coordination (cont.)

• The body carries out both voluntary and involuntary functions that depend on the nervous system.

• Automatic movements in response to a signal are called reflexes.

Control and Coordination (cont.)

Humans detect their external environment with five senses—vision, hearing, smell, touch, and taste.

Control and Coordination (cont.)

• Each of the five senses has specific neurons that receive signals from the environment.

• Information detected by the senses is sent to the spinal cord and then to the brain for processing and a response.

Control and Coordination (cont.)

The endocrine system, like the nervous system, sends signals to the body.

Endocrine System

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• Chemical signals released by the organs of the endocrine system are called hormones.

• Hormones travel in blood through blood vessels and cause organ systems to carry out specific functions.

• Some hormones work with other organ systems to maintain homeostasis and other hormones work with many organ systems to help you grow.

Endocrine System (cont.)

• reproduction

• gamete

• sperm

• ovum

Reproduction and Development

• fertilization

• zygote

• Some of the organs of the endocrine system produce hormones that help humans reproduce.

• Reproduction is the process by which new organisms are produced.

Reproduction and Hormones

• Human reproductive cells, called gametes, are made by the male and female reproductive systems.

• Male gametes are called sperm.

• Female gametes are called ova, or eggs.

• A sperm joins with an egg in a reproductive process called fertilization.

Reproduction and Hormones (cont.)

The cell that forms when an egg and a sperm join together is called a zygote.

Reproduction and Hormones (cont.)

• The endocrine system controls egg maturation and release and thickening of the lining of the uterus in a process called the menstrual cycle.

• The menstrual cycle takes about 28 days and has three parts.

Reproduction and Hormones (cont.)

• During human development, the zygote develops into an embryo, which is a ball-shaped structure that attaches inside the uterus.

• The embryo develops into a fetus, the last stage of birth.

• During the developmental period, called pregnancy, the organ systems of the fetus will develop and the fetus will get larger.

Human Development