Post-it notes or pieces of paper and a pen for labelling
What to do
Set three glasses or jars on the counter.
Label one glass “water”, one “sugar water” and one “juice”
Pour one cup of water into the glasses labelled “water” and “sugar water”.
Pour one cup of juice into the last empty glass labelled “juice”.
Add ½ cup of sugar to glass labelled “sugar water” and stir for 5 minutes.
Put one gummy bear into each glass. Keep one gummy bear for comparison.
Put the glasses in the fridge and leave the gummy bears to soak overnight.
The next day use a spoon to take each gummy bear out of its glass.
Compare the gummy bears to the one you left outside. What happened to them? You can even use a ruler to measure the gummy bears.
All gummy bears are safe to eat. Compare how they feel when you eat them.
Each liquid contained more water and less sugar than the gummy bears. The water went into the gummy bears to balance out the amount of water between the bears and the solution. This movement of water from a place with lots of water to a place with less water is called osmosis. For example, plant roots use osmosis to take up water from the soil.
The gummy bears swelled up because water moved into them through osmosis. The larger the bear, the more water moved into it. How was osmosis different for the three liquids used?
You can watch a short video of this experiment here:
Use the knife to cut the bottom 3 cm and top 5 cm off each celery sticks.
Place one celery stick into a glass of coloured water immediately. There should be at least 3 cm of celery sticking up above the water.
Set the other celery stick on the counter to dry for 30 minutes.
After 30 minutes, place the second celery stick into the second glass of coloured water. There should be at least 3 cm of celery sticking up above the water.
Let both celery sticks soak overnight.
Observe what happens over the next two days.
Water is very important for plants. They use it for photosynthesis in their leaves to make their own food. The water that is used up in the leaves is taken from the soil and moves up through the plants – defying gravity! This movement of water in plants is called “transpiration”.
In this experiment, you can observe the water movement by tracking the coloured water in your celery. Do you think water movement in plants works better in dry or wet plants?
You can watch a short video with this experiment here:
When I got my vaccinations as a child, there was one particular immunisation that I still remember today. Unlike all other vaccines it was not administered as an injection (which I hated and am still squirmish about today). Instead, the doctor just put a few sweet, sugary drops in my mouth and told me to swallow them. This was my polio vaccination.
I still remember five-year old me thinking: Was that it already? Where is the syringe? Maybe they are trying to trick me and will sting me later?
Polio is caused by a virus that is spread from person to person. About 72 % of individuals who are infected with polio do not get ill at all. The rest often show flu-like symptoms like fever, tiredness, a sore throat or headache.
In a small proportion of patients, the polio virus moves into the spinal cord and nervous system. This can cause meningitis (an infection in the covering of the spinal cord and brain) and paralysis (the inability to move arms and/or legs). Paralysis, the most dreaded symptom, occurs in about 1 in 200 polio cases according to World Health Organization (WHO) estimates.
A person can die of polio if the paralysis includes a muscle called the ”diaphragm” which is located below the lungs. When the diaphragm muscle moves down the lungs fill with air. The air is pushed out of the lungs when the muscle moves up. If the diaphragm is paralysed patients loose the ability to breathe and suffocate.
The only way to save these patients’ life is to put them inside a machine called an ”Iron Lung” which breathes for them. This large apparatus encloses the whole body, leaving only the patient’s head outside. It uses pressure to inflate and deflate the lungs enabling the individual to breathe.
When recovering from polio some patients regain the use of their muscles and are be able to breathe and walk again. However, others never recover. Many have to continue using wheelchairs. Others spend the rest of their lives locked inside Iron Lungs.
Due to these horrible consequences, people in the Western world used to be terrified of polio in the first half of the 20th century. During local polio outbreaks, schools as well as places of worship would close and large gatherings were prohibited. Steps that sound only too familiar to today’s Covid-19 measures.
Another similarity between the two diseases is that many individuals do not get ill or only exhibit very mild symptoms which enables the wide spread of the disease. At the same time, other patients are hit very hard, die or suffer long-term repercussions. For polio, it was impossible to predict who would walk away with a light headache and who would have to spend the rest of their lives inside an Iron Lung.
In addition, as for Covid-19, there was an intense race to find a vaccine against polio. The first inactivated polio vaccine (IPV), which is given as an injection in arms or legs, developed by Jonas Salk, was approved 1955. Another oral polio vaccine (OPV), invented by Albert Sabin, came into use 1961. The latter was the vaccine that I received as a six-year old swallowing the sweet, sugary drops.
The introduction of the two polio vaccines was a huge success leading to the eradication of polio in large parts of the world. There have not been any new polio cases in the US since 1979 and in the UK since 1984. The Americas and the Western Pacific region were declared polio-free in 2000, India followed in 2014.
The latest part of the world to eradicate polio is Africa which has only been anounced recently, 25 August 2020, about seven years after the last new case was registered in Nigeria.
Only two countries remain were polio is still active, Pakistan and Afghanistan and eradicating the disease there seems to be only a question of time. We are almost there!
The large scale eradication of polio has been possible thanks to the vaccination programs of the WHO, Unicef and their partners. If you want to make a contribution to eradicating polio completely, you can donate polio vaccines through Unicef’s Online Shop.
The story of the eradication of polio gives hope that we will also be able to stop Covid-19. As with polio, much will depend on the development and use of vaccines. The images of rooms crammed with children in Iron Lungs are history today. The images of overfilled intensive care units with patients on ventilators will be history some day too, hopefully soon.
Image: Barbara McClintock in her laboratory in 1947. Credit: Smithsonian Institution.
Barbara McClintock was born 118 years ago, 16 June 1902, in Hartford, Connecticut (US). The girl showed great interest in science and research already from a young age. However, her family had little money and was skeptical. They thought that it was better for her to marry and be financially secure.
Nevertheless, her father, a physician, supported her wishes in the end and in 1919, McClintock started a degree in Biology at Cornell University, New York (US). Six years later, she received her Master’s degree and in 1927 her PhD in genetics and zoology.
During her PhD studies, McClintock started the research that would shape her entire career. She began investigating the DNA of corn. For this work, microscopes and colouring techniques were used to identify and analyse individual corn chromosomes. (= long strands of DNA found in each living cell). In 1933, McClintock and her colleague, Harriet Creighton, published important results showing that chromosomes are the basis of genetics.
We need to keep in mind that McClintock conducted these experiments long before the structure of DNA was even discovered in 1952. This gives us an idea about how difficult and sophisticated her work must have been.
After a spell at the University of Missouri (1936-1941), McClintock moved to Long Island, New York to work at the Cold Spring Harbor Laboratory. She would stay for the rest of her professional life and conduct her most important research here.
In the 1940s and 50s, McClintock experimented with the colours of kernels on corn. This work led to the discovery that genetic information is not fixed. McClintock isolated two genes (= short sections of DNA) that controlled kernel colour and showed that they could move along a chromosome to different places. She also proved that these changes could affect neighbouring genes on the chromosome.
In 1983, McClintock received the Nobel Prize in Physiology or Medicine ”for her discovery of mobile genetic elements”. Popular science would come to call these moving genetic elements ”jumping genes”.
Barbara McClintock died 2 September 1992 in Huntington, New York (US).
What do the squirrel and the tulip have in common?
Both have a mutation in the gene that codes for the protein responsible for their colour. The mutation causes the squirrel to be white and have red eyes. This condition is also called “albinism”. The tulip has a mutation in only one petal giving half of it a yellow colour.
A mutation is a change in a gene that creates a new version of the gene or allele. Mutations happen when there is a mistake in copying DNA during cell division.
For example, one base in a DNA sequence might be replaced with another, a bit like typing the wrong letter in a word. This can happen naturally, but is more likely to happen if DNA has been damaged by radiation or certain chemicals.
The change in the body caused by a mutation can be either positive, negative or have no effect at all. Most of the time mutations only have a small or no effect on the proteins that are produced and do not change how the body works.
The Human Genome Project
In 2003, the first complete human genome was decoded by the Human Genome Project. This project involved many scientists from different countries and produced the map of 3.3 billion base pairs in one set of 46 chromosomes. Your genome contains all the DNA that is found inside your cells.
Further work showed that 99 % of DNA is the same for very human. Mapping a person’s genome can show their risk for developing certain diseases like cancer. It can also help to identify which medicine might be best to treat that person. In addition, mapping the genome can provide information about which genetic disorders someone could pass on to their children.
What is a mutation and how does it occur?
Mutations happen naturally, but what makes them more likely to occur?
Are mutations positive, negative or none of the two?
Looking at the squirrel, is the mutation affecting its colour positive or negative? Why? (Tip: Think about predators.)
Looking at the tulip, is the mutation affecting its colour positive or negative? Why? (Remember, that the tulip needs to attract butterflies and bees.)
What was the Human Genome Project?
What is a genome?
How much percent of DNA is the same for every human?
Give three advantages of mapping a person’s genome.
Chromosomes are found inside the nucleus of cells and consist of long strands of DNA. Each human cell has 46 chromosomes (23 pairs), apart from gametes (sex cells) which have only 23.
You can think of chromosomes as a set of books. Each book (chromosome) contains a set of instructions (genes). All of the books together contain all the instructions needed to make a certain organism (a living thing), for example a human or a flower.
There are always two copies of the same gene in an organism because chromosomes come in pairs. These two versions of the same gene are called alleles.
The two alleles for one characteristic do not have to be the same. They can be different. If both alleles for one gene are the same, they are homozygous (from homo = the same). If the alleles are different, they are heterozygous (from hetero = different).
For example, everyone has two alleles of the gene that decides eye colour. If someone has brown eyes and is homozygous for that gene, they will have two alleles for brown eyes. We can see this for individual B in the middle of the image..
A person could also have brown eyes and be heterozygous for that gene. They have one allele for brown eyes and another allele for blue eyes. We can see this for individual A to the left in the image. The reason that this person has brown eyes is that alleles can be either dominant or recessive.
The gene for brown eyes is dominant and we will always see this characteristic, no matter what other gene is present. The gene for blue eyes is recessive and we only see it when the dominant gene for brown eyes is not present. We can see this for individual C to the right in the image.
Characteristics that we see on the outside are called the phenotype. The characteristics in our genes are called the genotype. Phenotype and genotype can be slightly different. In our example we have seen that someone can have brown eyes as their phenotype, but both brown and blue eyes in their genotype.
What are chromosomes and where are they found?
What are alleles?
What is meant by homozygous?
What is meant by heterozygous?
What is meant by dominant?
What is meant by recessive?
Why does a person have brown eyes even when they have genes for both brown and blue eyes?
What is meant by phenotype?
What is meant by genotype?
What is the phenotype (= the colour seen on the outside) of a rose that is homozygous and has two dominant alleles for red colour?
What is the phenotype of a rose that is homozygous and has two recessive alleles for white colour?
What is the phenotype of a rose that is heterozygous and has one dominant allele for red colour and one recessive allele for white colour?
DNA is found inside the nucleus of each cell. One very long, coiled up molecule of DNA is called a chromosome. Human cells have 46 chromosomes in total.
Each DNA molecule contains two strands that are connected by a pair of substances called bases. It looks like a ladder, where the bases form the rungs. In addition, the ladder is wound and looks a bit like a spiral staircase. We call this wound-ladder structure of DNA a “double helix”.
This double helix structure of DNA was discovered by the British scientists James Watson and Francis Crick who received the Nobel Prize for their work in 1962.
There are four bases in DNA, adenine, thymine, cytosine and guanine, normally just called A, T, C and G. When forming pairs to make the rungs of the ladder, A always pairs with T and C with G. We call this complementary base pairs. The base pairs are held together by a weak attraction called hydrogen bonding.
Furthermore, each base is attached to a sugar which in turn bonds to a phosphate group. The sugars and phosphate form the backbone of the DNA strands.
A gene is one section of DNA that codes for one single characteristic or protein. We all have very small differences in our genes caused by slightly different orders of the bases in our DNA. This means that everyone’s DNA is unique. It allows scientists to match DNA from cells to specific people. For example, it helps scientists to find out how people are related or it can be used by forensic scientists to identify criminals.
Where is DNA found?
What is a chromosome? How many chromosomes do humans have?
What does the structure of DNA look like? What do we call it?
Who discovered the structure of DNA?
Name the four bases in DNA.
What is complimentary base pairing?
What holds the base pairs together?
What is a gene?
Why is everyone’s DNA unique?
How can the knowledge that everyone’s DNA is unique help scientists?
Image credit: Copyright by Kenneth Allen. CC BY-SA 2.0. The image shows stinging nettle on the left and dock leaf on the right.
It is the 2020 Corona virus lockdown and I am teaching online from home. Trying to keep things a bit interesting I am putting together small experiments to do at home. While thinking about possible experiments for the topic ”Acids and Alkalis”, I remember something I was taught myself in primary school. The sap of dock leaves is supposed to relieve the symptoms of nettle stings.
Me and many other children around the world were taught that stinging nettles sting because their poison contains acids. The sap of dock leaves is supposed to help because it is alkaline and neutralizes (cancels out) the nettle’s acid.
Perfect! I thought and was very excited to have found a great activity for the children. Finding stinging nettles and dock leaves and investigating their properties at home.
However, I did some further reading and quickly realized that I would not be able to use this activity.
The leaves of stinging nettles are covered in tiny hairs. When you brush against them their tip breaks of and they turn into tiny needles injecting the venom into your skin. It is true that the venom contains acids like formic acid oxalic acid and tartaric acid. Nevertheless, scientists argue that their concentrations are too low to cause any pain.
Today the bad guys of nettle stings are believed to be three compounds that are found in our own bodies as well. Serotonin, acetylcholine and histamine. Serotonin and acetylcholine are produced by our nervous system where they carry messages between nerve cells. But when injected directly into our skin, they cause irritation and pain. Histamine is probably the worst of the trio, causing inflammation and allergic reactions to the skin. The effect or nettle stings is most likely due to a nasty combination of all three. However, in some nettle species tartaric acid and oxalic acid are thought to at least contribute to a longer duration of the pain.
Now we know that the pain and itching of nettle stings is not really caused by acids at all. But what about the alkali part? Is dock leaf sap really alkaline? The answer is no. It has also been suggested that dock leaves may contain antihistamines to cancel out the effect of the histamines, but there is no evidence for this either.
Image: Osmosis. The process plant roots use to take in water.
Plants use their roots to absorb (= take up) water and mineral ions from the soil. The water absorbed by plant roots is used for:
Transporting dissolved mineral ions
Keeping cells rigid (= stiff), so the plant stays upright
Cooling the leaves (when the water evaporates from them)
Root hair cells
The outside of roots is covered with root hair cells. The “root hair” is an extension of the cell and provides a larger surface area, so that water and mineral ions can be absorbed faster. In addition, root hair cells have very thin cell walls to improve the flow of water into the cells.
Diffusion and osmosis
Diffusion is the movement of particles from a place of high concentration to a place of low concentration. We say that the particles move along a concentration gradient.
Osmosis is the diffusion of water. Water particles move from a place with a high water concentration (lots of water) to a place with a low water concentration (less water). This happens across a semi-permeable membrane which lets small molecules like water pass, but keeps back larger molecules like sugar. The semi-permeable membrane acts like a sieve.
Root hair cells take in water from the soil using osmosis. The water moves from the soil with lots of water into the root with less water. Cell wall and cell membrane act as the semi-permeable membrane.
Mineral ions are ionic compounds or salts that are found naturally in soil. Plants need these ions to build important substances like proteins.
The concentration of mineral ions inside the root is higher than outside. Mineral ions cannot diffuse from a lower concentration outside to a higher concentration inside the root. Therefore, the cell membrane needs to actively pump mineral ions inside. This process requires energy and is called active transport.
What is the water absorbed by plant roots used for?
What process do plants need carbon dioxide, water and sun light for?
Give two adaptations (= special features) that root hair cells have to let water enter the cells faster.
What is the difference between diffusion and osmosis?
How does water enter root hair cells? What is the name of the process?
What is a semi-permeable membrane?
What are mineral ions?
What is active transport?
Why do mineral ions not diffuse into root hair cells?