Fundamental Concepts of Biology: Cells & Life Processes

Characteristics of Living Organisms

Movement

A change of position or place.

Respiration

A chemical process in which oxygen is used to release energy from sugar molecules. Most of it happens in the mitochondrion.

Sensitivity

The ability to detect or sense changes in the environment (stimuli) and to make responses.

Growth

A permanent increase in size by increasing cell number, cell size, or both.

Reproduction

The process that makes more of the same kind of organism.

Excretion

The removal of toxic materials, waste products, and excess substances from an organism.

Nutrition

The process in which nutrients are taken into the body and converted into simpler substances used for energy, growth, and tissue repair.

Cell Structure and Organization

Cells can be classified as:

• Prokaryotic: Cells that lack a membrane-bound nucleus.
• Eukaryotic: Cells that contain a membrane-bound nucleus. These include:
  • Animal cells
  • Plant cells

Eukaryotic Cells: Key Features

• Contain DNA in a membrane-bound nucleus, separate from the cytoplasm.
• All contain a large number of specialized membrane-bound organelles.
• Any eukaryotic cell has a cell membrane, nucleus, and cytoplasm.

Essential Eukaryotic Cell Components

Cell Membrane

It controls the passage of materials in and out of the cell, as it is partially permeable.

Nucleus

Controls the cell activities. Contains thread-like structures called chromosomes, which are mostly made of DNA.

Cytoplasm

It is a clear jelly made up of 70% water. It contains many substances dissolved in it, especially proteins. Many metabolic reactions take place there.

Plant Cells: Unique Characteristics

Plant cells typically have a regular shape, a cell wall, chloroplasts (in most), and a large central vacuole.

Key Plant Cell Components

Cell Wall

Found only in plant cells. It is made of cellulose and helps to protect the cell. It is fully permeable.

Vacuole

It is a space in a cell surrounded by a membrane and contains cell sap. Full vacuoles press outwards on the rest of the cell, helping to keep it in shape. Animal cells have smaller vacuoles or none at all.

Chloroplasts

Never found in animal cells, but present in most plant cells. They contain chlorophyll, which absorbs energy from sunlight and uses it to make plant food through photosynthesis. Chloroplasts often contain starch grains.

Magnification in Biology

Magnification Formula: Picture size ÷ Actual size

Unit of Measurement: Micrometer (µm)

• 1 cm = 10 mm
• 1 mm = 1000 µm