CELL THEORY 7 th grade science

UNDERSTANDING CELLS English scientist Robert Hooke invented the microscope around Hooke observed a piece of bark from a cork tree and saw cells for the first time! He thought the cells he observed under the microscope looked like rooms in a monastery which were called “cells” Soon, other scientists began improving on the microscope and they looked for cells in other places

EARLY DISCOVERIES BY SCIENTISTS Matthew Schleiden, a German scientist, used a microscope to observe plant cells Theodore Schwann, also a German scientist, began to study animal cells under a microscope. Schleiden and Schwann made comparisons and realized that the cells had similar features and carry on similar functions, such as extracting energy from food and eliminating wastes. From this observation, the scientists concluded that cells are the basic unit of life. Two decades later, Rudolf Virchow proposed that all cells come from pre-existing cells The observations from the 3 scientists were combined into what is now known at the CELL THEORY

THE CELL THEORY 1. All living things are made of one or more cells 2. The cell is the smallest unit of life 3. All new cells come from preexisting cells.

BASIC CELL SUBSTANCES WATER The main ingredient in a cell is WATER. Over 70% of a cell is water Water maintains homeostasis, or a stable internal environment Water is essential for life Substances must be in liquid to move in and out of a cell – water is the ideal liquid

BASIC CELL SUBSTANCES MACROMOLECULES Macromolecules form when smaller molecules join together Are important for cells to function correctly Four main macromolecules: 1. Lipids – large macromolecule that does not dissolve in water ex: cholesterol, vitamin A 2. Carbohydrates – chains of sugar molecules. They store energy, provide structural support, and are needed to provide communication between cells. Ex: sugars and starches are carbohydrates that store energy 3. Nucleic acids – DNA and RNA: form when long chains of nucleotides join together. The order of nucleotides in DNA and RNA is important. Changing the order changes the genetic information. –DNA – contains instructions for cell growth, cell processes and cell reproduction. DNA makes RNA –RNA - makes protein 4. Proteins – long chains of amino acid molecules. Cells contain hundreds of proteins, each has a unique function. Proteins help cells communicate with each other, transport substances inside cells, break down nutrients, (ex: amylase in saliva), and provide structural support (ex: keratin: hair, horns and feathers).

THE CELL: SHAPE AND MOVEMENT The shape of the cell relates to the function it performs. Disk shaped red blood cells carry oxygen and travel through small blood vessels Nerve cells allow signals to be sent along dendrites to other nerve cells

MULTICELLULAR ORGANISMS CELL DIFFERENTIATION –Cells from a multicellular organism all start as one cell: a fertilized egg –Cell division starts rapidly after fertilization –The first cells made can become any type of cell: nerve cell, blood cell, muscle cell –The process by which cells can become different types of cells is called cell differentiation –The cell’s instructions are contained in its chromosomes –Different cell types use different parts of the instructions on the chromosomes

CELL DIFFERENTIATION

ANIMAL STEM CELLS Stem cells are unspecialized cells that are able to develop into many different cell types There are many stem cells in embryos, but fewer in adults

PLANT STEM CELLS Plant stem cells are unspecialized cells grouped into areas of a plant called meristems Cell division in meristems produces different types of plant cells with specialized structures and functions, such as transporting materials, making and storing food, or protecting the plant

TISSUES: ANIMALS Groups of cells that carry out a specific task Humans have 4 main types of tissues: –1. connective – connects, provides structure and support –2. muscle – causes movement –3. nervous – carries messages to and from the brain –4. epithelial – provides protective outer layer of the skin

TISSUES: PLANTS Plants have 3 main types of tissue: 1. dermal – provides protection 2. vascular – transports water and other nutrients 3. ground – provides storage and is where photosynthesis occurs

ORGANS: ANIMALS Complex jobs in an organism require more than one type of tissue Groups of different tissues working together to do a specific job Ex: heart, lungs, skin, stomach The stomach has all 4 types of tissues: Nerve – sends signal to brain “I’m full” Muscle – digests food Epithelial – lines the inside of the stomach and protects it Connective - supports the stomach wall

ORGANS: PLANTS Plants organs include the stems, roots and leaves Each has a specific job to do

ORGAN SYSTEMS: ANIMALS Groups of organs that work together to complete a task Ex: human digestive system is made of mouth, stomach, small intestine and large intestine

ORGAN SYSTEM: PLANTS Plants have 2 organ systems: Shoot system – food and water are transported throughout the plant by shoot system Root system – anchors the plant and takes in water and nutrients

ORGANISMS Multicellular organisms usually have many organ systems: Humans have the following systems: Digestive, endocrine, reproductive, skeletal, muscular, respiratory, nervous, integumentary, urinary, circulatory, immune, Each organ system depends on each other Example: cells in the muscle tissue in the stomach cannot survive without oxygen. The muscular system relies on the circulatory and respiratory system to provide oxygen.

ORGANIZATION OF LIVING THINGS

DNA – THE MOLECULE OF LIFE