Name: ______Date: ______Period: _____ Unit 2: Section 2: Characteristics of Life and Cells
Big Idea: Organisms share common characteristics of life. Cells have organized structures and systems necessary to support chemical reactions needed to maintain the living condition.
Essential Questions: How do we know if something is alive? What are the differences between prokaryotic and eukaryotic cells?
Biology is the study of life. But what is life?
No single characteristic is enough to describe a living thing. Also, some nonliving things share one or more traits with organisms. Some things, such as viruses, exist at the border between organisms and nonliving things.
Despite these difficulties, we can list characteristics that most living things have in common. Both fish and coral, for example, show all the characteristics common to living things.
1. Living things are made up of one or more cells. The smallest units considered fully alive.
Cells can grow, respond to their surroundings, and reproduce. Despite their small size, cells are complex and highly organized. For example, a single branch of a tree contains millions of cells.
Cell - The basic unit of structure and function for all living organisms. Cells have three common components: genetic material, cytoplasm, and a cell membrane. Eukaryotic cells also contain specialized organelles.
The Cell Theory A fundamental concept of biology that states that all livings things are: 1. composed of cells 2. that cells are the basic units of structure and function in living things 3. and that new cells are produced from existing cells.
Many living things consist of only a single cell and are called unicellular organisms. Plants
Unit 2 Section 2 Page 1 and animals are multicellular. Cells in multicellular organisms display many different sizes, shapes, and functions.
Eukaryotic vs. Prokaryotic Cells Eukaryote: A type of organism composed of one or more cells containing a membrane‐bound nucleus, specialized organelles in the cytoplasm, and a mitotic nuclear division cycle. Examples: all animals and plants
Prokaryote: A single‐celled organism that lacks a membrane‐bound nucleus and specialized organelles. Example: bacteria
2. Living things can reproduce.
Sexual Reproduction – type of reproduction in which cells from two parents unite to form the first cell of a new organism.
Asexual Reproduction – process of reproduction involving a single parent that results in offspring that are genetically identical to the parent.
3. Living things grow and develop.
During development, a single fertilized egg divides again and again. As these cells divide, they differentiate, which means they begin to look different from one another and to perform different functions.
Other growth indicators: getting larger, adding new material to replace existing parts, changing functions, aging, ultimately leading to death.
4. Living things obtain and use material and energy to grow, develop, and reproduce.
Metabolism - the combination of chemical reactions through which an organism builds up or breaks down materials.
For example, leaves obtain energy from the sun and gases from the air. These materials then take part in various metabolic reactions within the leaves.
5. Living things respond to their environment.
Stimulus- is a signal to which an organism responds.
For example, some plants can produce unsavory chemicals to ward off caterpillars that feed on their leaves.
Unit 2 Section 2 Page 2 6. Living things maintain a relatively stable internal environment, even when external conditions change dramatically.
All living organisms expend energy to keep conditions inside their cells within certain limits. Homeostasis is the regulatory process in which an organism regulates its internal environment.
Regulation of Resources Thermoregulation- the ability of an organism to keep its body temperature within certain boundaries, even when the surrounding temperature is very different.
Oxygen Regulation- the physiological regulation of oxygen in plants and animals.
Water Regulation- the management of water, mostly concerned with conservation of water, within the individual cells of an organism and throughout the body.
7. Living things are based on a universal genetic code.
All organisms store the complex information they need to live, grow, and reproduce in a genetic code written in a molecule called DNA.
That information is copied and passed from parent to offspring and is almost identical in every organism on Earth.
8. Living things evolve or change over time.
Evidence of this shared history is found in all aspects of living and fossil organisms, from physical features to structures of proteins to sequences of information in DNA. Evolutionary theory is the central organizing principle of all biological and biomedical sciences.
For example, signs of one of the first land plants, Cooksonia, are preserved in rock over 400 million years old.
Unity and Diversity of Life Life takes a variety of forms. Yet, all living things are fundamentally similar at the molecular level.
All organisms are composed of a common set of carbon-based molecules, store information in a common genetic code, and use proteins to build their structures and carry out their functions. Unit 2 Section 2 Page 3 Evolutionary theory explains both this unity of life and its diversity.
Vocabulary homeostasis metabolism water regulation eukaryote stimulus oxygen regulation prokaryote sexual reproduction thermoregulation cell asexual reproduction cell theory
Unit 2 Section 2 Page 4