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Watch this for an introduction to Chemistry of life!

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500 possible mastery points

About this unit

In this unit, we'll explore the foundations of life itself, learning about macromolecules from proteins to nucleic acids. By the end, you'll have a better understanding of the chemical properties that make life possible.

Level up on the above skills and collect up to 240 Mastery points Start quiz

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AP® is a registered trademark of the College Board, which has not reviewed this resource.

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Chemistry of life | AP®︎/College Biology | Science | Khan Academy

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In this unit, we'll explore the foundations of life itself, learning about macromolecules from proteins to nucleic acids. By the end, you'll have a better understanding of the chemical properties that make life possible.

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Look at these links for an introduction to cells.

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Cell Biology contains problem sets, tutorials and activities on Studying Cells, Cell Cycle and Mitosis, Meiosis, Prokaryotes, Eukaryotes and Viruses, the Cytoskeleton, Online Onion Root Tips: Phases of the cell cycle, and WWW Resources. The Biology Project, an interactive online resource for learning biology developed at The University of Arizona. The Biology Project is fun, richly illustrated, and tested on 1000s of students. It has been designed for biology students at the college and high school level, but is useful for medical students, physicians, science writers, and all types of interested people.

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Cool Genetics introduction!!

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Genetics 101 (Everything You Learned in High School) - Gene Food

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Genetics 101: a quick refresher of the basics of genetics. Everything you learned in high school about DNA, but forgot. 10 minute read.

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Ecology - Environmental interactions

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Ecology is the study of how organisms interact with one another and with their physical environment.

Ecology is studied at many levels, including organism, population, community, ecosystem, and biosphere.

Welcome to ecology!

Have you ever hiked through a forest and noticed the incredible diversity of organisms living together, from ferns to trees to mushrooms the size of dinner plates? Or taken a road trip and watched the landscape change outside the window, shifting from oak forest to tall stands of pine to grassy plains? If so, you've gotten a classic taste of ecology, the branch of biology that examines how organisms interact with each other and with their physical environment.

Ecology isn't just about species-rich forests, pristine wilderness, or scenic vistas, though. Have you, for instance, ever found cockroaches living under your bed, mold growing in your shower, or even fungus creeping in between your toes? If so, then you've seen equally valid examples of ecology in action.

Biotic and abiotic factors

One core goal of ecology is to understand the distribution and abundance of living things in the physical environment. For instance, your backyard or neighborhood park probably has a very different set of plants, animals, and fungi than the backyard of a fellow Khan Academy learner on the opposite side of the globe. These patterns in nature are driven by interactions among organisms as well as between organisms and their physical environment.

As an example, let's go back to our shower mold. Mold is more likely to appear in your shower than, say, your sock drawer. Why might this be the case?

Maybe the mold needs a certain amount of water to grow, and this amount of water is found only in the shower. Water availability is an example of an abiotic, or nonliving, factor that can affect distribution of organisms.

Maybe mold feeds off of dead skin cells found in the shower, but not in the dresser. Availability of nutrients provided by other organisms is an example of a biotic, living-organism-related, factor that can influence distribution.

Case study: the red panda

Let's apply the idea of biotic and abiotic factors to another organism, one that a field ecologist might be likely to study. Red pandas are distant relatives of raccoons and are found only in the eastern Himalayas. They spend most of their time in trees and eat a primarily vegetarian diet. In recent years, the red panda population has dropped significantly, leading conservation groups to classify it as a vulnerable or endangered species.

What are the main factors behind this change in abundance? Ecologists have found that biotic factors, such as logging of trees and introduction of diseases from domestic dogs, played a major role in the decline of red panda populations. Abiotic factors have been less important to date, but changing temperatures could cause further habitat loss in the future.

Understanding the main factors responsible for the decline in red panda numbers helps ecologists form conservation plans to protect the species.

How do ecologists ask questions?

To ask questions about the natural world-such as, "Why is the red panda declining?"-ecologists draw on many areas of biology and related disciplines. These include biochemistry, physiology, evolution, behavioral biology, and molecular biology, as well as geology, chemistry, and physics.

Natural historians were arguably the first ecologists-dating back to the Greek philosopher Aristotle! However, today's ecologists are rigorous, quantitative scientists. They run controlled experiments, use statistics to find patterns in large datasets, and build mathematical models of ecological interactions.

Ecology at many scales

Within the discipline of ecology, researchers work at five broad levels, sometimes discretely and sometimes with overlap: organism, population, community, ecosystem, and biosphere.

Let's take a look at each level.

The five levels of ecology are listed above from small to large. They build progressively-populations are made up of individuals; communities are made up of populations; ecosystems are made up of a community plus its environment; and so forth. Each level of organization has emergent properties, new properties that are not present in the level's component parts but emerge from from these parts' interactions and relationships.

The levels of ecological study offer different insights into how organisms interact with each other and the environment. I like to think of these levels as magnifying glasses of different strengths. If you really want to get what's going on in a particular ecological system, you'll likely want to use more than one!

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What is ecology? (article) | Ecology | Khan Academy

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Learn for free about math, art, computer programming, economics, physics, chemistry, biology, medicine, finance, history, and more. Khan Academy is a nonprofit with the mission of providing a free, world-class education for anyone, anywhere.

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Bacteria and Virus differences

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Both bacteria and viruses are invisible to the naked eye and cause your sniff, fever or cough, so how can we tell the difference?

With bacteria rapidly developing resistance to antibiotics, it is increasingly important that we know the distinction, because viruses can't be treated with antibiotics, nor bacteria with antivirals.

Rapid and effective testing is imperative, so we can successfully treat the offending microorganism.

COVID-19 is teaching us the hard way-we have no treatment for a new virus until we have anti-viral drugs and vaccines specifically targeted against it.

Therapies developed against an existing virus often do not work, or work poorly, against a new virus. Until this time, our best weapons are handwashing and physical distancing.

On a biological level, the main difference is that bacteria are free-living cells that can live inside or outside a body, while viruses are a non-living collection of molecules that need a host to survive.

Many bacteria help us: living in our gut digesting and helping absorption of our food, fixing nitrogen and decomposing organic materials in soil. Similarly, not all viruses are bad-we now know there are also beneficial viruses present in our gut, skin and blood that can kill undesirable bacteria and more dangerous viruses.

Bacteria and viruses are all around us

What are bacteria?

Bacteria are free-living cells that can live inside or outside a body.

Bacteria are prokaryotes-the smallest, simplest and most ancient cells, with free-floating genetic material. These microscopic single-celled organisms can be rod, spiral or spherical in shape.

There are two types of bacteria: Gram-negative and Gram-positive. The key difference is the presence of an extra outer membrane in Gram-negative bacteria. It's essentially an extra line of defence that makes it harder for antibiotics to penetrate, thus making Gram-negative bacteria more difficult to kill and more prone to developing resistance.

Bacteria are abundant in soil, inhabiting plant root systems to provide services like nitrogen fixing or acting as antifungal agents. Thermophilic (heat-loving) bacteria fix sulphur to produce sulphide and energy for photosynthesis in aquatic sediments or organically rich waters.

Dangerous bacteria live in soil, a good reason to wear gardening gloves.

Dangerous bacteria also live in soil, a good reason to wear gardening gloves. The floods in northern Queensland in 2019 brought Burkholderia pseudomallei to the surface, bacteria which cause a serious infection known as melioidosis.

In our bodies, bacteria inhabit the human digestion system, live on our skin and contribute to energy metabolism, digestion, brain function and general wellbeing. But if the balance of these bacteria is tipped by a dose of antibiotics or ill-health, then gut discomfort or skin infections are common.

Infectious diseases caused by bacteria have killed well over half of all humans who have ever lived on Earth. Historically, bacterial infections have started major pandemics such as the bubonic plague, which is estimated to have killed 50-60 per cent of the population of Europe during the Black Death in the 14 th Century.

Bacteria reproduce mainly by binary fission

Communication is key

Bacteria can communicate with one another by releasing chemical signalling molecules, allowing the population to act as one multicellular organism.

Depending on the density of molecules and the signal it generates, the bacterial community can adapt and respond to compete for resources in a process known as quorum sensing.

Communication gives bacteria some of the qualities of higher organisms.

This ability to communicate with one another allows bacteria to coordinate gene expression, and therefore the behaviour, of the entire community.

This process gives bacteria some of the qualities of higher organisms and is a powerful weapon against antibiotics. It can trigger some bacteria to shut down and become dormant when exposed to an antibiotic, and they are able to regenerate when the antibiotic is gone.

What are viruses?

Viruses are an assembly of different types of molecules that consist of genetic material (either a single- or double-stranded DNA or RNA) with a protein coat and sometimes a layer of fat too (an envelope).

They can assume different shapes and sizes-spacecraft designs, spirals, cylinders and ball shapes.

Viruses that are enveloped with a layer of fat (such as SARS-CoV-2 which causes COVID-19) can be more readily killed by simple handwashing, because soap disrupts this fatty layer.

Viruses can't reproduce on their own (unlike bacteria) so they aren't considered 'living', but they can survive on surfaces for a varying level of time.

Viruses are a non-living collection of molecules that need a host to survive.

Viruses need to enter a living cell (such as a human cell) to be able to reproduce, and once inside they take over all of the cellular machinery and force the cell to make new virus.

Viruses cause diseases including the flu, herpes simplex virus, Ebola, Zika and the formidable common cold.

Viruses can be quite selective about where they live and reproduce-many viruses don't even infect humans. Some viruses only infect bacteria, some only infect plants, and many only infect animals.

However, a virus can evolve to jump into humans. This often happens with influenza: for example bird flu or swine flu which originated in birds and pigs and managed to infect humans. SARS-CoV-2, the virus that causes COVID-19, probably jumped into humans from bats.

The life cycle of a virus can be divided into the following stages: entry of the virus into the host cell; replication of the viral genome; production of new viral proteins; assembly of those viral proteins into new viruses and then release from the host cell (either by killing the cell or by budding off the host cell membrane) ready to infect new cells.

The goal is for quick tests to be available in the GP surgery.

Vaccines show the immune system important parts of the virus so that the immune system can prepare the tools to fight the real virus effectively-vaccines trick the immune system into responding like it has previously seen the virus.

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What's the difference between bacteria and viruses?

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Both bacteria and viruses are invisible to the naked eye and cause your sniff, fever or cough, so how can we tell the difference? With bacteria rapidly developing resistance to antibiotics, it is increasingly important that we know the distinction, because viruses can't be treated with antibiotics, nor bacteria with antivirals.