1. www.soran.edu.iq M. Saadatian INTRODUCTION: THEMES IN THE STUDY OF LIFE 1

2. www.soran.edu.iq INTRODUCTION: THEMES IN THE STUDY OF LIFE

3. www.soran.edu.iq Biology: the study of life A characteristic of life is a high degree of order. Biological organization is based on a hierarchy of structural levels, with each level building on the levels below it.

4. www.soran.edu.iq 1. Order. Organisms are highly ordered, and other characteristics of life emerge from this complex organization. 2. Reproduction. Organisms reproduce; life comes only from life (biogenesis). 3. Growth and Development. Heritable programs stored in DNA direct the species-specific pattern of growth and development. 4. Energy Utilization. Organisms take in and transform energy to do work, including the maintenance of their ordered state. 5. Response to Environment. Organisms respond to stimuli from their environment. 6. Homeostasis. Organisms regulate their internal environment to maintain a steady-state, even in the face of a fluctuating external environment. 7. Evolutionary Adaptation. Life evolves in response to interactions between organisms and their environment.

5. www.soran.edu.iq Cells are an organism’s basic units of structure and function 1.Lowest level of structure capable of performing all activities of life. 2.All organisms are composed of cells. 3.May exist singly as unicellular organisms or as subunits of multicellular organisms. 4.Cells are bounded by plasma membranes that regulate passage of materials between the cell and its surroundings. 5.All cells, at some stage, contain DNA.

6. www.soran.edu.iq Based on structural organization, there are two major kinds of cells: prokaryotic and eukaryotic. Prokaryotic cell = Cell lacking membrane-bound organelles and a membrane-enclosed nucleus. Found only in the archaebacteria and bacteria Generally much smaller than eukaryotic cells Contains DNA that is not separated from the rest of the cell, as there is no membrane-bound nucleus Lacks membrane-bound organelles Almost all have tough external walls

7. www.soran.edu.iq Eukaryotic cell = Cell with a membrane-enclosed nucleus and membrane-enclosed organelles. Found in protists, plants, fungi, and animals Subdivided by internal membranes into different functional compartments called organelles Contains DNA that is segregated from the rest of the cell. DNA is organized with proteins into chromosomes that are located within the nucleus, the largest organelle of most cells. Cytoplasm surrounds the nucleus and contains various organelles of different functions Some cells have a tough cell wall outside the plasma membrane (e.g., plant cells). Animal cells lack cell walls.

8. www.soran.edu.iq The continuity of life is based on heritable information in the form of DNA Biological instructions for an organism's complex structure and function are encoded in DNA. Each DNA molecule is made of four types of chemical building blocks called nucleotides. The linear sequence of these four nucleotides encode the precise information in a gene, the unit of inheritance from parent to offspring. An organism's complex structural organization is specified by an enormous amount of coded information. Inheritance is based on: A complex mechanism for copying DNA. Passing the information encoded in DNA from parent to offspring.