What is an organism?

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Table of Contents

Chapter: Life's Structure and Classification Section 1: Living Things

What is an organism? Any living thing is called an organism. Organisms vary in size: one-celled or many-celled (unicellular or multicellular)

*All living things have similar traits that determine what it means to be alive. 1. Composed of cells and have an internal organization 2. Living things grow and develop 3. Can reproduce 4. Maintain internal balance ( homeostasis) 5. Need energy to survive ( comes from food) 6. Respond to stimuli from the environment

What is a cell? A cell is the smallest unit of an organism that carries on the functions of life. *Cells are the building blocks of life.

Living Things have an internal organization

This internal organization is found in unicellular eukaryotic organisms and in all cells that are part of multicellular organisms. Cells have internal structures surrounded by membrane, called organelles, responsible for particular functions

Prokaryotic cell - no internal membrane, nor organization - simple organism Euglena - eukaryotic unicellular organism with a simple internal organization some organelles are present Multicellular organisms have millions of eukaryotic cells - with internal membrane and internal organization (organelles).

*In a Multicellular organism: Each cell carries on its own life functions but also performs a job for the whole organism. Ex: Muscle cell – perform a job for the organism – help with the contraction of the muscle and provide the necessary energy for this contraction A muscle cell, also needs to perform basic functions to be alive.

*Levels of Organization in a multicellular organism:

Cells – tissues- organs – organ systems – whole organism

** All the functions that organisms perform to survive, are also performed at a cellular level – respiration, digestion, elimination of waste materials…. All the functions performed by an organism are possible because of functions performed by their cells

*All living things have similar traits that determine what it means to be alive. 1. Composed of cells and have an internal organization 2. Living things grow and develop 3. Can reproduce 4. Maintain internal balance ( homeostasis) and respond to stimuli 5. Need energy to survive ( comes from food)

How do organisms grow? • Growth of a many-celled organism is mostly due to an increase in the number of cells. • In one-cell organisms, growth is due to an increase in the size of cell.

Life Span • Length of time an organism is expected to live. • Humans – 80 years • Some insects – live one day • Some pine trees can live 4600 years

*All living things have similar traits that determine what it means to be alive. 1. Composed of cells and have an internal organization 2. Living things grow and develop 3. Can reproduce 4. Maintain internal balance ( homeostasis) and respond to stimuli 5. Need energy to survive ( comes from food)

Why do Living Things Reproduce ? All living things reproduce, to make more of their own kind. *The main goal of any living organism is to reproduce to guarantee the survival of the species

*All living things have similar traits that determine what it means to be alive. 1. Composed of cells and have an internal organization 2. Living things grow and develop 3. Can reproduce 4. Maintain internal balance ( homeostasis) and respond to stimuli 5. Need energy to survive ( comes from food)

How do organisms maintain internal balance? Through a process called Homeostasis

DEFINITION: Homeostasis is a series of mechanisms responsible for maintaining internal balance of an organism, despite changes in the environment EX: Homeostasis keeps our body temperature constant

Stimulus and Response: • A stimulus is anything that changes in the environment that can affect the organism’s internal equilibrium. • The reaction to a stimulus is a called a response and responding to stimuli is important for the survival of this organism.

Ex: Stimulus - a drop in the external temperature. What would be the responses???? because of Homeostasis, your body will:

1) start shaking shaking – produces heat and warms up your body 2) vasoconstriction – superficial veins contract, lowering the body surface exposed to the outside your body loses less heat Both responses try to maintain the ideal body temperature ( part of your equilibrium)

*All living things have similar traits that determine what it means to be alive. 1. Composed of cells and have an internal organization 2. Living things grow and develop 3. Can reproduce 4. Maintain internal balance ( homeostasis) and respond to stimuli 5. Need energy to survive ( comes from food)

How do organisms obtain E? The energy used by most organisms comes either directly or indirectly from the Sun. *Some are producers- they make their own food by using the energy from the sun or from chemical substances (also called autotrophs) *Others will eat the producers to obtain the energy ( consumers or heterotrophs)

What do living things need to survive? 1) a place to live with enough space to grow and hide 2) water – needed for many basic cell functions 3) Food – give them energy All living organisms need proteins, minerals, vitamins, carbohydrates ( sugars) and fat to survive and organisms take in these materials when they eat.

**What differentiates plants from animals? • Plants can make their own food and animals can’t • Plants take in carbon dioxide and release oxygen, animals do the opposite • Animals can move and plants can’t • Unlike animals, plants have little to none ability to sense • Plant and animal cells are different