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If someone were to ask you what biology was, how would you reply? Biology is quite a complex concept to explain. Does it study plants, animals and humans only, or does it cover much more than that? StudySmarter’s Biology Revision and Notes will show you that biology is the study of life. In fact, it is the study of ALL life and even some things that are classified as not living – viruses, for instance. Biological study starts from the smallest atoms and molecules, such as carbon atoms in the proteins that digest our food. Biology then examines larger structures, such as tissue, organs, and whole organisms, including bacteria, viruses, plants, animals, and humans. It continues with the study of topics including genetic diversity, the evolution of species, and ecosystems.

Our planet Earth is one massive, incredible ecosystem! It is packed with various forms of life, from the smallest microorganisms to plants and large animals. These forms of life interact with one another; they move, reproduce, and live in oceans, grass, cities, villages, etc. Imagine you are standing on the top of a mountain, looking down at all this diversity. That is all included in the study of life, i.e. biology. Impressive, isn’t it?

Biology topics and learning objectives

On StudySmarter, you will find vital resources for your biology courses. We follow specifications developed by expert teachers of biology. This way, we ensure our content is high-quality and relevant to all who embark on a learning journey with StudySmarter. Most biology courses cover the following topics:

  • Biological molecules.

  • Cells.

  • Substance exchange.

  • Genetic information.

You’ll find those on StudySmarter, but we also offer you these topics as well:

  • Energy transfers.

  • Responding to change.

  • Genetics, populations, evolution and ecosystems.

  • Control of gene expressions.

Let’s introduce all the biology topics.

Biology: Biological molecules

Biological molecules are carbon-based compounds essential for most biological processes.

Biological molecules serve as the structural components of molecules and cells, such as simple carbohydrates in bases of DNA and RNA and complex carbohydrate cellulose in plant walls. Moreover, biological molecules called lipids build cell membranes, forming a phospholipid bilayer. Some biological molecules, like proteins, act as enzymes, messengers and hormones, carrying out metabolic functions. Nucleic acids, DNA and RNA, carry the genetic information in all living things and viruses. The other two essential biomolecules are ATP (adenosine triphosphate) and water, necessary for cellular processes.

Biology Revision and Notes Biological Molecules diagram StudySmarterDiagram of a molecule. Source: Canva

Biology: Cells

Cells are the smallest units of life. The study of cells is one of the most significant in biology.Cells can be either prokaryotic or eukaryotic. They contain genetic material and divide to create new cells. Eukaryotic cells divide with processes called mitosis and meiosis. Prokaryotic cells divide by binary fission.

Cells vary in the number and type of organelles, which are subunits inside all cells. One of the essential structural components of the cell is the cell surface or plasma membrane. It serves as a protective layer and is the main player in transporting vital substances in and out of cells. Specialised cells called T lymphocytes and B lymphocytes are crucial for our immune systems. These cells aid in the fight against diseases.

Biology Revision and Notes Cells StudySmarterEukaryotic cells: an animal cell and a plant cell. Source: by brgfx.

Biology: Substance exchange

Substance exchange in biology is the exchange of substances (e.g. glucose) between the internal and external environments of cells.

This is how organisms get oxygen and nutrients from the external environment and get rid of metabolic waste. Multicellular organisms require specialised organ systems for substance exchange because their surface area to volume ratio is too small to rely on cell membranes as an exchange surface.

Substance exchange in plants is called a mass flow system. The mass flow systems of plants comprise xylem and phloem. Substance exchange in animals happens in different organ systems, including the digestive, respiratory, and circulatory systems. Digestion and absorption of nutrients occur in the digestive system, whereas gas exchange takes place in the respiratory system. The circulatory system pumps and circulates blood that carries nutrients and oxygen. This role of the circulatory system is crucial to ensure the high metabolic activity of cells for all of the organ systems in the body to function properly.

Biology Revision and Notes Substance Exchange Human Heart StudySmarterDiagram of the human heart. Source:

Biology: Genetic information

DNA is a remarkable molecule consisting of our genetic material. Genetic material is involved in every aspect of biology, making DNA an essential molecule for the continuation of life.

The DNA in the nucleus is organised into genes made of nucleotides, which are found on chromosomes. Sometimes, the order of these nucleotides goes wrong, and mutations occur. Different mutations have different effects on the organism, but one of the beneficial effects is introducing genetic diversity into a species. Genetic diversity is also achieved during meiosis (a type of cell division) which allows DNA to be switched around so that the sex cells (also called gametes) have a different combination of DNA.

As a result of this vast genetic diversity in organisms, we have millions of species that we need to organise and classify. This is the study of taxonomy. Complementary to genetic diversity is the biodiversity we see in communities. We can quantify this level of diversity using measurements such as the index of biodiversity and species richness.

Biology Revision and Notes Genetic Information DNA and RNA StudySmarterDNA and RNA. Source:

Biology: Energy transfers

The term energy transfer refers to the changes in energy that occur in and between organisms within an ecosystem.

All life depends on energy, which is usually derived from the Sun. The transfer of this energy between different organisms allows them to maintain their highly ordered environments and communities.

When it comes to how energy is transferred, there are two types of organisms: autotrophs, including plants, lichens or algae, and heterotrophs, including animals and humans. Most autotrophs gain energy from the Sun via photosynthesis. This process involves autotrophs using light energy to turn carbon dioxide and water into glucose and oxygen. Heterotrophs cannot synthesise their own energy and rely on acquiring it through consuming other organisms. They perform an inverse process to photosynthesis: they take glucose and oxygen and turn them into carbon dioxide and water. This energy transfer is called respiration.

Biology Revision and Notes Energy Transfers Photosynthesis StudySmarterPlants use the energy from the Sun for photosynthesis. Source: Canva

Biology: Responding to change

Organisms respond to change in the internal and external environments. The change comes in the form of a stimulus. The stimuli (singular stimulus) can be a physical or chemical change and are recognised by specialised cells called receptors. The response to the stimuli is crucial for the survival of species. Neurones or nerve cells are cells specialised for transporting nerve impulses. There are millions of neurones in mammals, making up the complex and fascinating nervous system. Some of the organs coordinated by the nervous system are the muscles. Contraction of skeletal muscles starts with an action potential reaching and travelling deep into muscle fibres, ultimately triggering the sliding filament mechanism. All these responses to changes are necessary for the body to maintain a constant internal environment. This is called homeostasis. Living organisms require a consistent temperature, pH, and an overall chemical balance to function.

Biology Revision and Notes Responding to Change Synapse and transmission of nerve impulses StudySmarterDiagram of a synapse and the transmission of nerve impulses. Source:

Biology: Genetics, populations, evolution and ecosystems

Individual members of one species have the same set of genes but can vary in combinations of alleles. Alleles are different forms of a gene responsible for the genetic diversity in species. The more alleles in the genome of a species, the greater the genetic diversity. When members of one species live together in a habitat, they form populations. These, in turn, form communities where diverse species cohabit and interact with one another. The population size can vary and is affected by biotic (living) and abiotic (non-living) factors. For instance, competition and predation within or between different species are biotic factors, while the pH and temperature in the species’ habitat are abiotic factors.

Communities and the environment they inhabit make up ecosystems. An ecosystem is a self-sustaining, dynamic system that includes all living organisms (biotic part of the ecosystem) and the physical environment (abiotic components).

Biology Revision and Notes Genetics and Ecosystem animals and plants in a habitat StudySmarterA varied ecosystem with animals, plants and their habitat. Source: by macrovector

Biology: Control of gene expression

Some of the DNA in our cells can contain mutations. Considering all cells start off with the same genome, how can they have different functions and features, i.e. mutations? It is because of different levels of gene expression. Some genes in the genome are switched ‘on’, meaning they are expressed, and the proteins they code for are made, while other genes are switched ‘off’, meaning the corresponding protein is not synthesised.

Mutations can affect the level of expression, but epigenetics also plays a significant role. Epigenetics investigates the modifications made to DNA and their associated proteins and how this affects the level of gene expression. Other influencing factors include processes happening before transcription and before and after translation.

These investigations into DNA and genes require remarkable gene technologies, which have been used to develop advanced medical techniques such as gene therapy and forensic technology such as genetic fingerprinting.

 Biology Revision and Notes Control of Gene Expression investigating DNA and genes StudySmarterA scientist investigating DNA and genes. Source: Canva

How can StudySmarter support me in studying Biology?

Whether you are revising the topics covered in your biology course or studying for your upcoming exams, StudySmarter has got you covered. Our original, efficient, smart, and interactive learning system allows you to master biology like never before. What’s more, it’s all free! What is the secret? How do we do it? To find out more, follow our Biology Revision Guide.

Biology Revision and Notes StudySmarter Support for Biology exams StudySmarterpch.vector at, edited in Canva

The Biology Revision Guide

Our intelligent guide is here to introduce everything you need to know to revise your biology courses and exams successfully. Here is what you can discover on StudySmarter:

Biology summaries

StudySmarter biology summaries cover all you need to know about essential topics in biology, introducing interesting facts that will deepen your understanding and appreciation of the subject. Did you know that a human heart goes through a cardiac cycle that is only 0.8 seconds long?You can also become a creator yourself by uploading your biology coursework: summaries, workbooks, notes, and more.

Biology flashcards

Flashcards are a fantastic feature helping you learn in an easy and fun way. Biology flashcards contain questions and answers on topics covered in the summaries. Did you know that you can create your flashcards with particular questions YOU want to practice? How cool is that!

Biology study groups

You don’t have to stop at creating and uploading your material. StudySmarter lets you form study groups and learn with your friends and biology students from wider learning communities. Remember the flashcards? You can use them to quiz fellow group members and test their knowledge. This way, you can create a personalised Biology quiz! Learn, create, quiz – repeat.

Rewards for learning Biology

StudySmarter is your next best friend, encouraging you to learn and achieve top results. StudySmarter lets you set your weekly goals: complete subjects, correctly answer flashcards, ask questions. Reaching these goals will earn you trophies. For example, gain the Best thing since sliced bread if you study every week for three months, or become a Grandmaster if you answer five questions in the same course. The more you learn, the more trophies you get to celebrate your hard work.

Biology Revision and Notes Rewards for learning Biology StudySmarterStudySmarter trophies: earn while you learn!Source: by makyzz, edited in Canva


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