ORGANIZATION IN PLANTS AND ANIMALS

ORGANIZATION IN PLANTS AND ANIMALS

reflect

What is your body made of? You might say that you are made of atoms or cells. You might even say you are made of organs, like skin and a heart. These answers are all correct. Each focuses on a different level of organization of the human body. Atoms are a nonliving unit of the body. But cells and organs are living units. How do these different living units relate to each other? Where do body systems, like the digestive system, fit into these levels of organization?

Organization in Animals In all living things, the cell is the smallest unit of life. Some organisms are unicellular. They are made of a single cell functioning on its own. Bacteria and yeasts are two examples of single celled organisms.

Animals are multicellular, meaning they are

composed of more than one cell. In fact, the human

body is made up of about 100 trillion cells! Cells

have a variety of different shapes and structures

because they each have a different function. For

example, muscle cells tend to be long to allow for

contraction. Nerve cells tend to have many branches

to help with communication. One main function of

red blood cells is to transport oxygen from the lungs

to other cells throughout the body. An important

function of certain bone cells is to release hormones

Nerve cells have many

that help form bones.

branches that help them send

signals throughout the body.

Cells that are similar in structure and function

form tissues. The cells that make up tissues work

together to perform a specific activity. Animals have four main types of tissue:

? Muscular tissue is involved in movement. For example, skeletal muscles help move the body. The stomach has smooth muscle tissue, which helps to churn foods and break the foods down into smaller pieces. The smooth muscle of the stomach can also expand to hold large amounts of food and then relax when empty.

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ORGANIZATION IN PLANTS AND ANIMALS

? Epithelial tissue is found on the surface of organs and lines the inner spaces of the organs. This tissue type also covers the entire body because it forms skin. The main functions of epithelial tissue are protection, secretion (producing and releasing materials) and absorption (taking in materials). Epithelial tissue that lines the stomach secretes chemicals that help with digestion.

? Nervous tissue functions to sense stimuli from the environment and send signals throughout the body. For example, nervous tissue in the stomach sends signals to the

stimuli: things that an organism can sense

brain to let a person know when he or she is hungry. Nervous

tissue also works with muscle tissue to help the body move. For example, when you

touch a hot object, the nervous tissue in your hand sends signals to the brain to contract

your muscles in order to move your hand away.

? Connective tissue has a variety of functions. This type of tissue connects and holds together structures in the body, providing support and structure. Connective tissue includes bones and fat tissue. Connective tissue is also found under epithelial tissue and helps to support the cells of the epithelial layer. In the stomach, connective tissue can be found under its epithelial tissue also.

The next level of organization in animals is the organ. Each organ is made of tissues with similar structure and function. Examples of organs include the heart, skin (the largest human organ), lungs, and stomach.

The organ systems are the next level of organization. An organ system consists of two or

more organs working together to perform a specific function for the organism. The human

body is organized into several main organ systems: circulatory, nervous, skeletal, muscular,

integumentary, endocrine, digestive, immune, reproductive, excretory, and respiratory

systems. Each system performs specific functions. For example, the integumentary system

is made of the skin, hair, nails, and glands. This system receives stimuli from the external

environment and protects the body's deeper tissues and organs. The digestive system is

made of a number of organs. The stomach stores food and

helps with digestion. The intestines digest food and absorb nutrients. The liver works as part of the digestive system by secreting bile, which is a substance that helps with the break down of fats, or lipids. A single organ can work with multiple organ systems. For example, the liver also works with the circulatory system to filter wastes in the blood.

glands: organs that make and release chemicals called hormones; hormones control and regulate body processes

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ORGANIZATION IN PLANTS AND ANIMALS

The final and most complex level of organization in animals is the organism. Organisms are entire living things that perform basic life processes. Organisms take in materials, release energy from food, release wastes, grow, respond to the environment, and reproduce.

Simple

The living units of organization from smallest to largest are cells, tissues, organs, organ systems, and organisms. The images here show, from left to right, are an epithelial cell, epithelial tissue, a stomach, the digestive system, and a human body. Note that the images are not to scale.

Complex

what do you think?

Suppose one organ in an organ system failed to work properly. How would the organ system be affected? Would it still be able to function? Explain your reasoning.

look out!

Not all animals have the same levels of organization. For example, sponges are simple aquatic animals. They are multicellular; however, their cells are not organized into well-defined tissues. They do not have organs or organ systems. A sponge's essential life functions are carried out on the cellular level.

Getting Technical: Magnetic Resonance Imaging

Magnetic Resonance Imaging, or MRI, is a procedure

used by doctors to help diagnose organ or organ

Sponges commonly live and

system diseases. The procedure uses magnets and

grow on coral reefs.

radio signals to generate images of the inside of the

body. The magnets and the radio signals in an MRI

machine interact with the water in a patient's body. The machine is then able to measure

how much water is present in any given area. This creates an image with various shades of

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ORGANIZATION IN PLANTS AND ANIMALS

grey from light (where there is a lot of water) to dark (where there is little water). Because the magnetic coils are able create a magnetic force encircling the entire body, the MRI machine is able to image the body in three dimensions, or in 3-D. This is displayed as a series of pictures showing one slice of the body at a time. Doctors examine the images to look for structural abnormalities that may be present in the organs.

An MRI machine generates a magnetic force that encircles the entire body.

An MRI machine generated this image of the brain and other structures.

Organization in Plants Like animals, plants are made of specialized cells that are organized into tissues. For example, xylem is a tissue that moves water, while the phloem is a tissue that moves sugars.

Plant tissues are organized into tissue systems. Plants have three tissue systems:

? The dermal tissue system covers the outside of the plant and provides protection. The dermal tissue system includes epidermal tissue and tiny openings, called stomata, that open and close to allow for gas exchange.

? The ground tissue system is a general tissue system with a variety of functions including photosynthesis and food storage. The ground tissue contains the photosynthetic cells (chloroplasts) of the plant.

These plant cells group together to form tissue.

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ORGANIZATION IN PLANTS AND ANIMALS

? The vascular tissue system is the system responsible for the transport of materials, including water and nutrients, throughout the plant. Xylem and phloem are parts of the vascular tissue system.

what do you think?

Which tissue system in plants is most similar to the integumentary system in animals? Explain your reasoning.

Plant tissue systems are organized into organs. Plants have four main organs: ? Leaves are the main organs used to capture sunlight used in photosynthesis. ? Roots are the main organs used to absorb water and nutrients from the soil. ? Stems are the main organs used to transport materials between leaves and roots. ? Reproductive organs (like flowers) produce seeds that grow into new plants. Flowers usually consist of colorful petals that attract insects and other pollinators.

Plant organs group together to form the two main organ systems of plants: the root system and the shoot system. The root system is typically underground and includes the root and associated fibers that branch off the main root. This system functions to anchor the plant and absorb water and nutrients from the soil. The shoot system is typically above the ground and includes the stem, the leaves, and the reproductive organs, such as flowers. This system has many functions including photosynthesis and reproduction. As with animals, the organ systems of plants work together to make up the structure and function of the entire organism.

The general organization in plants, from smallest to largest units, is shown below.

cells

tissues

tissue system

organ

organ system

organism

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