Characteristics of Living Things & The Necessities of Life

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Characteristics of Living Things Living things have cells. All living things are composed of one or more cell. A cell is a membrane-covered structure that contains all of the materials necessary for life. Plants and animals have different types of cells. Most cells are too small to be seen with the naked eye.

Living things sense and respond to change Living things sense and respond to change. A change that affects the activity of the organism is called a stimulus. Even though an organism’s outside environment may change, conditions inside the body must stay the same. The maintenance of a stable internal environment is called homeostasis. Your body does this through sweating when you are too hot, and twitching your muscles when you are too cold. Some animals can’t do this and must change their environment.

Reproduction and DNA Living things reproduce. Sexual reproduction – two parents produce offspring that will share characteristics of both parents. Most plants and animals do this. Asexual reproduction – a single parent produces offspring that are identical to the parent. Most single cell organisms reproduce in this way. Living things have DNA. DNA (deoxyribo-nucleic acid) controls the structure and function of cells. When organisms reproduce, they pass copies of their DNA to their offspring. This is why offspring resembles their parents. The passing of traits from one generation to the next is called heredity.

Living Things Use Energy & Grow An organisms metabolism is the total of all the chemical activities that an organism performs. Breaking down food, building cells, etc. Living things grow and develop. All living things, one cell or more, grow during periods of their lives. In addition to getting larger, living things may develop and change as they grow.

What do we need to live? Almost every organism has the same basic needs: water, air, a place to live, and food.

Water Your body is made up of mostly water. Almost all living organisms are composed of approximately 70% water. Organisms differ greatly in terms of how much water they need and how they get it. Humans can only survive for about 3 days without water, and get water from the fluids we drink and the food we eat. Some animals get water only from the food they eat.

Air Air is a mix of several different gasses, including oxygen and carbon dioxide. Most living things use oxygen to breathe and to release energy from their food. Plants, algae, and some bacteria need carbon dioxide and water to produce food and oxygen through photosynthesis. Almost all living things need air, but some do not. Organisms that can live without air are anaerobic organisms. They will not grow in the presence of air.

A place to live All organisms need a place to live that contains all of the things they need to survive. Some animals need a large amount of space, while others may stay in one place their whole life. Since space on earth is limited, organisms often compete with each other for food, water, homes, and other necessities.

Food All organisms need food, but they get it in different ways. They can be grouped into three different groups based on how they get their food. Producers – an organism that can make its own food by using energy from its surroundings. Plants are producers, they make their own food. Consumers – an organism that eats other organisms or organic matter. Humans, dogs, cats, frogs, etc. are all consumers. They need to eat to get food. Decomposers – organisms that get energy by breaking down the remains of dead organisms or animal remains. They consume or absorb the nutrients. Mushrooms are decomposers.

Nutrients Though all animals get food in different ways, they all need the nutrients found in food to live. Nutrients are made up of molecules, which are substances made when two or more atoms combine. Molecules made of different kinds of atoms are called compounds. Molecules found in living things are usually made of combinations of 6 different elements: carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur. These combine to make proteins, carbohydrates, lipids, AATP, and nucleic acids.

Proteins & Carbohydrates Proteins – Almost all of the life processes of a cell involve proteins. Proteins are large molecules that are made up of smaller molecules called amino acids. Organisms break down the proteins in food to supply their cells with amino acids, which are then linked together to form new proteins. They can be very simple or very complex. Carbohydrates – are a class of molecules that includes sugars, starches, and fiber; contains carbon, hydrogen, and oxygen. Cells use carbohydrates as a source of energy and for energy storage. There are two types. Simple – made up of one sugar molecule or a few sugar molecules links together. Table sugar and sugar in fruits are simple carbohydrates. Complex – When an organism has more sugar than it needs, its extra sugar may be stored as complex carbohydrates. made up of hundreds of sugar molecules linked together. Plants store extra sugar in starch.

Lipids Lipids are compounds that cannot mix with water. Fat molecules that include oils, waxes, and steroids. All cells are surrounded by a cell membrane that help protect the cell. Phospholipids are the molecule that form much of the cell membrane. Fats and oils are lipids that store energy. When an organism has used up most of its carbs, it can get energy from these lipids. At room temp most fats are solid (usually found in animals), and most oils are liquid (usually found in plants)

ATP & Nucleic Acids ATP - Adenosine triphosphate, also called ATP, is a molecule that acts as the main energy source for cell processes. Energy from carbs and lipids are transferred to ATP. Nucleic Acids – sometimes called the blueprints of life because they have all the information needed to a cell to make proteins. Large molecules made up of molecules called nucleotides. The order of these stores information. DNA is a nucleic acid.