Photosynthesis Explained

Understanding Photosynthesis

• Photosynthesis is the process where plants use light energy to create their own food.
• The word "photosynthesis" combines "photo" (light) and "synthesis" (making), meaning "making with light."
• Plants convert carbon dioxide and water into glucose, releasing oxygen as a byproduct, in the chloroplasts of their cells.
• Chloroplasts contain chlorophyll, which captures sunlight to power the reaction.

The Photosynthesis Equation

• The balanced chemical equation is: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
• Six carbon dioxide molecules and six water molecules are converted into one glucose molecule and six oxygen molecules using light energy.

Essential Requirements for Photosynthesis

• The three key requirements are water, carbon dioxide, and light energy.
• Water is absorbed by roots and transported to leaves via the xylem.
• Carbon dioxide is taken in from the air through stomata in the leaves.
• Light energy is captured by chlorophyll within chloroplasts.
• Captured light energy bonds water and carbon dioxide to form glucose, an energy source for the plant; oxygen is released.

Photosynthesis as the Foundation of the Food Chain

• Plants convert light energy into chemical energy stored in carbohydrates.
• These carbohydrates are the energy source for herbivores, supporting carnivores and omnivores.
• Without photosynthesis, the food web would collapse.

Oxygen Production and Atmospheric Balance

• Nearly all the oxygen in Earth's atmosphere is a product of photosynthesis.
• Plants, algae, and photosynthetic bacteria continuously replenish oxygen, essential for cellular respiration.

Regulation of Carbon Dioxide Levels

• Plants absorb atmospheric carbon dioxide, controlling global carbon levels.
• They act as carbon sinks, reducing greenhouse gas concentrations and helping maintain climate equilibrium.

The Role of Photosynthesis in Earth's Evolution

• Earth's atmospheric composition has been shaped by photosynthesis, with little initial free oxygen.
• Cyanobacteria began releasing oxygen ~2.5 billion years ago, leading to the Great Oxygenation Event.
• Oxygen now constitutes about 21% of Earth's atmosphere, supporting complex life forms.

Experiment 1: Collecting Oxygen Produced During Photosynthesis

• An aquatic plant in water is covered with an inverted funnel and test tube to collect gas.
• Oxygen bubbles collect in the test tube during photosynthesis.
• A glowing splint relights when inserted in the test tube, confirming the presence of oxygen.

Experiment 2: Investigating the Effect of Light Intensity on Photosynthesis

• A light source is placed at varying distances from an aquatic plant in a test tube.
• The number of oxygen bubbles produced in a given time is recorded for each distance.
• Higher light intensity generally increases the rate of photosynthesis, as more energy results in more oxygen.

Experiment 3: Testing a Leaf for Starch (Iodine Test)

• A leaf is boiled in water to kill cells, then heated in ethanol to remove chlorophyll.
• The leaf is rinsed and placed on a white tile, and iodine solution is added.
• A blue-black color confirms the presence of starch, indicating photosynthesis occurred.
• A brown or yellow color indicates the absence of starch.

Leaf Structure and Its Role in Photosynthesis

• The waxy cuticle prevents water loss.
• The upper epidermis allows light to pass through.
• The palisade layer contains many chloroplasts.
• The spongy mesophyll has air spaces for gas exchange.
• Stomata on the lower epidermis allow gas exchange.
• Guard cells regulate stomata opening and closing based on environmental conditions.

The Role of Minerals in Photosynthesis and Plant Growth

• Magnesium is needed for chlorophyll production, and nitrates are needed for proteins.
• Mineral deficiencies lead to stunted growth and reduced photosynthetic efficiency.
• Fertilizers are used to supplement these nutrients in agriculture.

Feeding

• Carbon enters the food chain through plants or other animals.
• Carbohydrates(glucose, starch, cellulose) is produced in plants through photosynthesis, which animals use for energy and growth.
• Herbivores consume plants; carnivores eat herbivores, transferring carbon.

Respiration

• Respiration is where glucose and oxygen produce energy (ATP), carbon dioxide, and water..
• The chemical equation is C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP).
• Decomposers respire and break down organic matter, releasing CO₂.

Decomposition

• Decomposers (bacteria and fungi) feed on dead plants and animals.
• They break down complex molecules into simpler compounds, releasing CO₂ through respiration.
• Decomposition recycles nutrients, including carbon, into the environment.

Photosynthesis

• Plants absorb carbon dioxide and use sunlight to make carbohydrates.
• The chemical equation is 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.
• Plants produce their own food using inorganic carbon sources.

Fossil Fuel Formation (Very Slow Process)

• Dead organisms in oxygen-free environments do not fully decompose.
• Over millions of years, heat and pressure transform them into fossil fuels (coal, oil, natural gas).
• Coal forms from ancient swamp plant material.
• Oil and natural gas form from tiny marine organisms on the seabed.

Combustion

• Burning fossil fuels releases stored carbon as carbon dioxide.
• The general equation is Fuel + O₂ → CO₂ + H₂O + energy.
• Combustion increases atmospheric CO₂ levels, leading to global warming.

Hydrogencarbonate Indicator and CO₂ Levels

• The indicator detects carbon dioxide concentration by color change.
• Purple indicates no carbon dioxide (alkaline).
• Red indicates low carbon dioxide concentration (neutral).
• Yellow indicates high carbon dioxide concentration (acidic).

Climate and Long-Term Temperature Patterns

• Climate is long-term patterns of temperature, wind, and precipitation.
• Earth has experienced warm periods with no polar ice and cold periods (ice ages).

Historical Climate Events

• 1st Ice Age (~2 billion years ago): Significant temperature drop and ice coverage.
• Snowball Earth (~650 million years ago): Earth was covered in ice and snow.
• Asteroid-Induced Ice Age (~470 million years ago): Dust clouds from asteroid collisions blocked sunlight.
• Dinosaur Extinction (~67 million years ago): Asteroid impact blocked sunlight, leading to ecosystem collapse.

Asteroids, Meteors, and Potential Threats to Earth

• Asteroids are orbit the sun.
• Meteoroids are small asteroid fragments in space.
• Meteors are meteoroids entering atmosphere.
• Meteorites are the remains of meteors on Earth's surface.
• Risk assessment considers mass, diameter, and closest approach to Earth.

Effects of Climate Change

• Higher Temperatures happen in atmosphere.
• Disrupted rain patterns impact agriculture.
• Sea levels rise from thermal expansion and melting ice.

Excretion

• Excretion is the removal of waste from internal body processes.
• It excludes digestive waste (faeces) that are not assimilated into the body.
• Key wastes include carbon dioxide, urea, and excess water.

The Excretory System Process

• The liver converts excess protein into urea, which is transported in the bloodstream.
• Kidneys filter out urea and excess water from the blood, forming urine.
• Urine travels via the ureter to the bladder.
• It is then expelled through the urethra.

Fetus and Pregnancy

• The fetus depends on the mother for nutrients and waste removal.
• Exchange of substances happens via blood.
• Nutrients and oxygen diffuse from mother to fetus, waste diffuses from fetus to mother.

Importance of a Balanced Diet During Pregnancy

• Protein for cell growth, muscle maintenance, and hemoglobin production.
• Carbohydrates, especially glucose, as essential energy sources.
• Iron supports haemoglobin production.
• Calcium supports bones and teeth.

Harmful Substances During Pregnancy

• Tobacco smoke (carbon monoxide, nicotine, tar) restricts fetal growth.
• Carbon monoxide reduces oxygen-carrying capacity.
• Certain drugs can be harmful to fetal health.

Recommendations to promote maternal and fetal health during pregnancy:

• Women should taking medication should consult with their doctor or pharmacist.
• Smoking cessation is essential.
• Avoid alcohol consumption.
• Strict prohibition of Illegal drug use.
• Reduce or eliminate caffeine intake.

Chromosomes & Genes

• Different species have chromosomes:
  • Humans have 46.
  • Fruit flies have 8.
  • Mango trees have 40.
• Chromosomes are numbered by length and consist of hundreds to thousands of genes.
• Genes are DNA segments controlling characteristics.
• DNA is a double-helix molecule containing instructions for cell functions.
• DNA structure was discovered in the 1950s.

Sperm Cell & Egg Cell

Fertilization & Sex Determination

• Fertilization of sperm cell with the egg creates a zygote.
• Sperm and egg each have 23 chromosomes.
• A zygote has 46 chromosomes.
• Sex chromosomes determine sex: XX is female, XY is male.
• Y chromosome is smaller than X chromosome.

Inheritance & Genetic Variation

• Inheritance is DNA passing from parents.
• Sex inheritance is transmission of X or Y chromosomes.
• Variation is differences between individuals; genetic differences are DNA variations.
• Fertilization creates combinations of DNA, resulting in identities.

Natural Selection & Evolution

• Variation is due to differences in genes.
• Variations provide survival advantages.
• Individuals with an higher chance to survival.
• Advantageous traits become common; disadvantageous traits become rare.
• This process is known as natural selection, and is also the driving force of evolution.

Antibiotic Resistance & Evolution in Bacteria

• Antibiotics treat bacterial infections.
• Resistance occures as bacteria may have mutations.
• These bacteria survive.
• These survivors reproduce, and pass on the resistance genes.
• The end result is some infections become harder to treat as antibiotics lose effectiveness.