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Biology

Biology is a natural science concerned with the study of life and living organisms. Anything that is living is studied in biology. The word biology comes from the Greek word bios, which means life, and logos, which means study and knowledge. Biology is the study of living things in order to gain knowledge of how they work. We split it into different branches to make it easier.

Branches of biology

• Taxonomy: The science of classifying living things into different families.
• Anatomy: The study of internal structure of organs.
• Cytology: The study of cells and how they function.
• Histology: The study of tissues.
• Paleontology: The study of fossils.
• Embryology: The study of embryos, which are entities that will develop into offspring.
• Genetics: The study of heredity and variations.

In biology, the cell is the basic unit of life. It is the most basic element in living things. It is able to replicate independently, so we often call it the building block of life. Genes are the basic unit of heredity, and evolution is the engine that propels the synthesis and creation of new species.

What does it mean to be alive?

An animal, person, or plant is considered to be alive when it performs self-sustaining processes like eating, sleeping, and reproducing. In order for things to be considered living, they have to perform certain processes. These include nutrition, respiration, excretion, locomotion, reproduction, growth, and response.

• Nutrition: As opposed to inanimate objects like rocks, living things have to feed on a variety of substances to get the nutrients their bodies need.
• Respiration: We all need to breathe in order to perform activity. Even though insects don’t have lungs, they still perform respiration, the same with fish that live underwater.
• Excretion: The metabolic activities in our body generate waste products that we have to get rid of.
• Locomotion: In order to carry out activities, living things have to move around in a controlled way, even plants, which move slowly in order to face the sun better.
• Reproduction: Living things have to reproduce new offspring, or else their species will not survive.
• Growth: Every living thing has to use the nutrition they collect in order to increase their size and grow stronger.
• Response: Living things must be sensitive to external stimuli and respond to them, like moving away from hot climates or protecting themselves from danger.

Characteristics of the five kingdoms of living things

The very simplest living things belong to the kingdom monera. Many monera are of microscopic size. There are about 3,000 different types or species of monerans. About half the species of monerans are bacteria, while the other half are primitive plant-like organisms known as blue-green algae. All monerans are unicellular, meaning they possess just one cell. Moneran’s cells are unique because they lack a nucleus. The nucleus is typically a rounded structure found only in cells of non-monera organisms. In animals, plants, fungi, and protists, the nucleus is where most of the information-storing DNA is located. However, because monerans lack a nucleus, their DNA is spread around inside their cells. Another characteristic of monerans is that their cells are surrounded by a thick outer cell wall. Cell walls are found only in monerans, fungi, and plants. Some monerans, in particular the blue-green algae, can manufacture food using the sun’s energy; such organisms are called autotrophs. Other monerans, including most bacteria, cannot make their own food; these organisms are called heterotrophs. To review, the characteristics of monerans are that they are unicellular, lack a nucleus, have cell walls, and can be either autotrophic or heterotrophic.

The next kingdom of living things, the kingdom Protista, consists of microscopic plant-like and animal-like creatures that are often referred to as protozoa. The kingdom Protista has about 30,000 species. All protists are unicellular; they have a nucleus but lack cell walls. Like the monera, some can make their own food and are autotrophic, while others are heterotrophic and cannot make food.

The members of the kingdom Plantae are multicellular organisms. This means they are made from many cells. Plant cells have both a nucleus and a cell wall. Plants are autotrophs and are able to use the sun’s energy to make their own food. There are about 285,000 species of plants.

The members of the kingdom Fungi—the mushrooms, molds, and yeasts—are also multicellular organisms. However, unlike plants, fungi are heterotrophs and cannot make their own food. Fungi cells have cell walls and almost always have more than one nucleus. There are about 100,000 species of fungi.

The final kingdom, the kingdom Animalia, is the biggest one. There are over 1 million species of animals. Animals are heterotrophs and cannot make their own food. Like plants and fungi, animals are multicellular organisms, but animal cells lack cell walls and have just one nucleus.

The cell

Every living thing is made up of cells. Cells are very small; so small you almost always need a microscope to see them. All cells are made of atoms. Atoms are much smaller than cells. All cells are surrounded by a sort of skin, called the cell membrane or plasma membrane. The jelly-like stuff inside the cell, surrounded by the skin, is generally called the cytoplasm. Inside the cell are tiny organs—called organelles—little organs. Those organelles are themselves surrounded by membranes. There are many different kinds of organelles, like the nucleus, ribosomes, mitochondria, and the Golgi apparatus. All the little organs of a cell—the organelles—work together to keep it alive. There are microorganisms made of a single little cell.

Every single living cell contains some very complicated stuff—some instructions—that tell the cell what to do. This stuff is called deoxyribonucleic acid. It is also called DNA. DNA is the command center of the cell.

In the cells of humans, other animals, and plants, the most important organelle is called the nucleus, and it is important because that’s where the DNA is. But some other cells do not have a nucleus. They do have DNA; it is just floating around in the cell, in the cell’s cytoplasm. Cells that have a nucleus are called eukaryotic cells. Cells that don’t have a nucleus are called prokaryotic cells. Eu- means they do; pro- means they don’t. As mentioned, humans, other animals, and plants all have eukaryotic cells, cells with nuclei. There are also microorganisms, single-celled organisms like tiny animals and plants, which have eukaryotic cells. These are also called protists. All microorganisms, all single-celled organisms, have prokaryotic cells. They are called prokaryotes. One example is the bacterium. So bacteria, like the kind in your yogurt and your stomach, are single-celled organisms without nuclei; they are prokaryotes. Most prokaryotes, like bacteria, not only don’t have nuclei, they don’t have any membrane-surrounded organelles. Some of them do have little hairs or tails.

Plant cells

Trees, flowers, vegetables, or fruit are made up of plant cells. These are in charge of the growth cycle. More specifically, vegetables make their own food through photosynthesis. A plant cell is a eukaryotic cell. The nucleus is in charge of all cell functions. DNA is stored in the nucleus. DNA is made up of genes, which hold genetic information. When plants reproduce, the genetic material will pass on to the new plant. For this reason, new plants will have the same characteristics. The membrane is a layer that surrounds and protects the cells from the outside environment. The main function of the membrane is to allow food in and release waste substances. Membranes have rigid wall cells that hold up the plant. The cytoplasm is a fixed solution found inside the membrane. Organelles are located in the cytoplasm. Chloroplasts are the organelles that produce and store chemical components essential to the cell; for example, chlorophyll, which gives plants their green color, is stored in the chloroplasts. Chlorophyll also plays an important role in photosynthesis. The mitochondria is the organelle in charge of producing energy.

Differences and similarities between plant and animal cells

There are similarities and differences between plant and animal cells.

Similarities

They are both considered eukaryotic cells because they both contain a nucleus and membrane-bound organelles. They have many of the same organelles; they both contain a rough and smooth ER, Golgi body, and mitochondria. They both have ribosomes, which create proteins. Technically, ribosomes are not organelles because they are not membrane-bound. In addition, animal and plant cells contain a cytoskeleton and cytoplasm. Both plant and animal cells contain a cell membrane.

Differences

• Plant cells have a cell wall membrane; animal cells do not. The cell wall is a rigid outer covering of a plant cell that provides structure and protection.
• A plant cell has chloroplasts. They are the location of photosynthesis, which allows the plant to convert sunlight into sugar. The mitochondria found in the plant cell use this sugar to create energy. Animal cells do not have chloroplasts.
• Plants have a large central vacuole compared to an animal cell that contains smaller vacuoles.
• Plant cells do not have lysosomes, but animal cells do. Lysosomes help animals break down large molecules, old cell parts, and sometimes large macromolecules that get past the cell membrane.
• The cell wall of a plant keeps these large molecules out, and plant cells have lytic vacuoles that perform a similar function to lysosomes in animals.
• Plant cells contain plastids and animals do not have plastids. The plastids of plants take several forms.
• Plants do not have centrosomes, but animals do. Centrosomes are the microtubule organizing and construction center and help spindle fibers attach to the chromosomes during mitosis.

Our bodies are the ultimate factory. Every cell has a specific job to do and is shaped to do that job perfectly. A muscle cell is a muscle cell and only a muscle cell. A nerve cell will only ever be a nerve cell and a...