How do the nutrients in dead matter become available to leaves?

When something, whether its animals or plants dies, they are broken down by microorganisms (decomposers). These microorganisms are also called saprobionts. These secrete enzymes onto dead tissue, this is called extracellular digestion. They absorb products of digestion. Respiration by microorganisms produces carbon dioxide. Carbon dioxide is then taken into the leaves.

How can Global Warming effect crop yield?

Global warming is caused by an increase in carbon dioxide - so weirdly, global warming is kind of increasing our crop yields. This is because carbon dioxide is a limiting factor for photosynthesis, so if you increase the amount of carbon dioxide then you increase the amount of photosynthesis which can take place. More photosynthesis means a faster growth rate, more crops and a higher yield. 

What is the carbon cycle?

Carbon dioxide, or CO2 (excuse the missing subscript) is all around us, mainly in the air and water. Plants remove carbon dioxide from the atmosphere as they carry out photosynthesis. Once the carbon dioxide has entered the plant, it becomes carbon compounds within the plant tissues.

Plants are then eaten by animals (the primary consumers) - the carbon is passed on to those animals. It then gets passed on to each successive consumer. Of course, at some point, all of these organisms die - they leave behind carbon compounds in them. Microorganisms called decomposers then digest these carbon compounds. As they feed on dead organic matter, this is called saprobiontic nutrition.

The cycle continues as the carbon is returned to the air and water due to respiration. During respiration, carbon dioxide is released into the atmosphere.

There are times where carbon compounds end up where there's not decomposers - this might be deep oceans or bogs. This means that over millions of years, they are turned into fossil fuels by heat and pressure. When fossil fuels are burnt, the carbon is released - you might know this as combustion.

Movement of Blood around the Body | AS Level Biology Revision

Arteries:

AWAY from the Heart

to Arterioles

Veins:

BACK to the Heart

Link Arterioles to Veins - CAPILLARIES (tiny vessels)

Arterioles - small arteries

Control blood flow into the capillaries

Path (starting going AWAY from the heart)

• Arteries
• Arterioles
• Capillaries
• Veins
• Heart 

Try this mnemonic to help remember the order:

Awesome Andy Cares Very Heroically 

What is visual acuity?

Visual Acuity - The ability to tell apart points which is close together

This is a bit like the resolution of something, you talk about the resolution of an image or microscope. As far as a microscope, the resolution is the smallest distance at which two objects can be told apart.

In your eyes,  Rod cells give low visual acuity because many rods join to the same neurone which means light from two objects close together can't be told apart. In you eye, Rod cells are more sensitive, but cone cells (the other type of cells in your eyes) help you see more detail.

Why are rod cells so sensitive?

 

Check out my previous post on what photoreceptors are...


o effectively detect light, your eye has two types of photoreceptors, rod and cone cells. Rod cells are the most sensitive to light. They fire action potentials in dim light.




In your eye, many rod cells join one neurone. Essentially, this means that lots of weak signals can combine to reach the threshold and fire an action potential - in scientific terms: many weak generator potentials can combine to reach the threshold so an action potential is fired sooner.

This article specifically relates to AQA Biology Unit 5

What are photoreceptors?

Before you read this post, you might find it useful to check out my previous post on what a receptor is.


Photoreceptors are light receptors in your eye. Light enters through your pupil. Your eye cleverly adjusts the amount of light which enters the eye using the muscles of the iris.


The light rays are then focussed onto the retina (part of the eye which lines the inside of the eye). The retina contains photoreceptor cells which detect light - from here the light is pretty much turned into messages sent to your brain. One part of the retina - the fovea, contains lots of photoreceptors. Nerve impulses are sent from the photoreceptor cells to the brain via the optic nerve (a bundle of neurones).

Sickle Cell Anaemia

Sickle Cell Anaemia is a recessive genetic disorder, it's caused by a mutation in the haemoglobin gene. This causes an altered haemoglobin protein to be produced. This means the red blood cells become sickle shaped (concave) - not the typical shape you're probably aware of. The red blood cell's concave shape means they can't flow through capillaries easily like normal red blood cells can so the capillaries can become blocked - blood flow is then restricted. This can also bring up so many more issues like organ damage and periods of acute pain.

Some people can be carriers of the sickle cell gene, amazingly, carriers of the sickle cell gene are partially protected from malaria. Because of this advantageous effect, the frequency of the sickle cell gene have increased. Unfortunately this means the likelihood of inheriting two copies of the allele are increased - overall, this means sickle cell anaemia is more prevalent in these areas.
 

AS Revision - DNA Replication

Mitosis: (used for growth and repair, including the growth of the foetus)

2 daughter cells produced

Identical to original (parent) cell and to each other, unless a mutation occurs.

Importance:

• Increase in number of cells
• 2 haploid cells fuse to make a diploid cell
• Differentiation
• Replacing cells (when they're damaged or die new cells must form to be genetically identical to function effectively)

Interphase: (cell not dividing, when replication of DNA occurs)

• cell continues its normal function
• prepares to divide
• Cells DNA is unravelled and replicated - genetic content is doubled
• Organelles replicated so there's spares
• ATP content increased

Prophase:

• Chromosomes condense (they get shorter and fatter)
• Centrioles start moving towards opposite ends of the cell forming a network of protein fibres across it (forms the spindle)
• Nuclear envelope breaks down
• Chromosomes are free in the cytoplasm

Nuclear envelope: membrane around the nucleus

Centrioles: tiny bundles of protein

Metaphase:

• Chromosomes (each have two chromatids) line up along the middle of the cell
• become attached to the spindle via their centromere

Anaphase:

• Centromeres divide
• separating each pair of sister chromatids
• spindle contracts
• Pulls chromatids to opposite ends of the cell (first the centromere)

Telophase:

• Chromatids reach opposite poles on the spindle
• uncoil and become long and thin again
• They're now called chromosomes again
• Nuclear envelope forms around each group of chromosomes so there are now 2 nuclei
• Cytoplasm divides
• FORMING: 2 daughter cells genetically identical to the original cell and to each other

Mitosis is now finished and each daughter cell starts interphase and the whole cycle repeats.

Mitotic index = the number of cells carrying out mitosis (visible chromosomes)/ total number of cells on the slide

Cancer:

(result of uncontrolled cell division)

• cell growth and cell division controlled by genes
• cancer is a tumour that invades surrounding tissue
• cells keep on dividing to make more tissue (the tumourr)

Chemotherapy:

• prevent the synthesis of enzymes needed for DNA replication
• Not specific- can kill normal cells, steps taken to reduce the impact on normal cells
• A large portion of the tumor is removed using surgery
• Repeated treatments (ie not one big dose), treatment breaks in between. 

G1- cell growth and protein production

specifically for AQA Biology AS Unit 2