9th (Freshman) Biology Notes

Biology is the science of life, the study of everything from molecules within living cells to the effects of human activity on our planet.

Bolded words are vocab words!

Unit 1 (One)

1.1 What Is Science?

One goal of science is to provide natural and testable explanations for events in the natural world. Science also aims to use explanations supported by data to understand patterns in nature, and to make useful predictions about natural events.

1.2 Science In Context

Applying scientific information involves understanding the role of science context in society and its limitations.

1.3 Patterns Of Life

Living things are made up of basic units called cells, reproduce, are based on a universal genetic code, grow and develop, obtain and use materials and energy, respond to their environment, maintain a stable internal environment, and evolve, changing over time.

Made Up of Cells

Organisms are made up of small, self-contained units called cells. Cells are the smallest units of an organism that can be considered alive. Cells can grow, respond to their surroundings, and reproduce. Despite their small size, cells are complex and highly organized.

Reproduction

Organisms produce new organisms through reproduction. There are two basic kinds of reproduction: sexual and asexual. The vast majority of multicellular organisms reproduce sexually. In sexual reproduction, cells from two different parents unite to produce the first cell of the new organism. In asexual reproduction, the new organism has a single parent.

Based On the Universal Genetic Code

With asexual reproduction, offspring, and their parents have the same traits. With sexual reproduction, offspring differ from their parents in some ways. Biologists now know that the directions for inheritance are carried by a molecule called DNA. This genetic code, with a few minor variations, determines the inherited traits of every organism on Earth.

Growth and Development

All living things grow during at least part of their lives. For some single-celled organisms, such as bacteria, growth is mostly a simple increase in size. Multicellular organisms typically go through a process called development. During development, a single fertilized egg cell divides again and again to produce the many cells of mature organisms. As those cells divide, they change in shape and structure. This process is called differentiation because it forms cells that look different from one another and perform different functions.

Need For Materials And Energy

An organism uses energy and a constant supply of materials to grow, develop, and reproduce. Organisms also need materials and energy to stay alive. The combination of chemical reactions as it carries out its life processes is called metabolism.

Respond to the Environment

Organisms detect and respond to stimuli from their environment. A stimulus is a signal to which an organism responds. External stimuli, which come from the environment outside an organism, include factors such as light and temperature. In contrast, internal stimuli come from within an organism.

Maintaining an Internal Balance

Most organisms must keep internal conditions, such as temperature and water content, fairly constant to survive. The relatively constant set of conditions is called homeostasis. Often internal stimuli help maintain homeostasis. For example, when your body needs more water to maintain homeostasis, internal stimuli make you feel thirsty.

Evolution

Although individual organisms experience many changes during their lives, the basic traits they inherited from their parents usually do not change. As a group, however, any given kind of organism can evolve or change over time. Over a few generations, the changes in a group may not seem significant. But over hundreds of thousands or even millions of years, the changes can be dramatic. The ability of a group of organisms to change over time is important for survival in a world that is always changing.

Unit 2 (Two)- The Chemistry of Life

2.1 The Nature Of Matter

Atoms

The basic unit of matter is an atom. The subatomic particles that makeup atoms are smaller than the atom. An atom is the smallest part of a substance that cannot be broken down chemically. Each atom has a nucleus (center) made up of protons (positive particles) and neutrons (particles with no charge).

Protons and neutrons have about the same mass. However, protons are positively charged particles (+), and neutrons carry no charge at all. Strong forces bind protons and neutrons together to form the nucleus at the center of the atom.

Electrons

The electron is a negatively charged particle (−) with only 1/1840 the mass of a proton. Electrons are in constant motion in the space surrounding the nucleus. They are arranged in a series of shells or orbitals. The first shell can contain no more than two electrons, and the second shell, no more than eight. Atoms have equal numbers of electrons and protons and are electrically neutral because the opposite charges cancel out.

Chemical Bonds

The atoms in compounds are held together by chemical bonds. Bond formation involves the electrons that surround each atomic nucleus. The electrons in an atom’s outer shell that are available to form bonds are called valence electrons. The main types of chemical bonds are ionic bonds and covalent bonds.

Ionic Bonds- An Ionic Bond is formed when one or more electrons are transferred from one atom to another. Recall that atoms are electrically neutral when they have equal numbers of protons and electrons. A neutral atom that loses electrons becomes positively charged. A neutral atom that gains electrons has a negative charge. These positively and negatively charged atoms are known as ions.

Covalent Bonds- Sometimes electrons are shared by atoms instead of being transferred. Meaning that the moving electrons travel about the nuclei of both atoms, forming a covalent bond. When the atoms share one electron from each atom, a single covalent bond is formed. Sometimes the atoms share four electrons to form a double bond. In other cases, atoms can share six electrons, forming a triple bond. The structure that results when atoms are joined together by covalent bonds is called a molecule. The molecule is the smallest unit of most compounds.