Science Inc 8/9

1. Organelles: Structure and Function

Organelles are specialized structures within cells that carry out specific functions necessary for the cell's life processes. Here's a breakdown:

Key Organelles:

• Nucleus:

  • Structure: Double-membraned organelle containing chromatin.

  • Function: Stores DNA and controls cell activities like growth and reproduction.

• Mitochondria:

  • Structure: Double-membraned; inner membrane folds into cristae.

  • Function: Powerhouse of the cell; generates ATP through cellular respiration.

• Endoplasmic Reticulum (ER):

  • Smooth ER: Synthesizes lipids and detoxifies harmful substances.

  • Rough ER: Studded with ribosomes; involved in protein synthesis and folding.

• Golgi Apparatus:

  • Structure: Stacked, flattened membranes.

  • Function: Modifies, sorts, and packages proteins and lipids for transport.

• Ribosomes:

  • Structure: Made of rRNA and proteins, can be free in the cytoplasm or attached to rough ER.

  • Function: Synthesize proteins.

• Lysosomes:

  • Structure: Membrane-bound sacs containing digestive enzymes.

  • Function: Break down waste materials, foreign invaders, and damaged cell parts.

• Chloroplasts (in plant cells):

  • Structure: Double membrane, contains chlorophyll.

  • Function: Conducts photosynthesis to produce glucose and oxygen from sunlight, carbon dioxide, and water.

• Cytoskeleton:

  • Structure: Network of protein filaments (actin, microtubules).

  • Function: Provides structural support, facilitates movement of materials within the cell.

• Cell Membrane:

  • Structure: Phospholipid bilayer with embedded proteins.

  • Function: Regulates the passage of substances into and out of the cell; provides protection and structure.

2. Mitosis: Cell Division for Growth and Repair

Mitosis is a type of cell division that produces two identical daughter cells. It's essential for growth, repair, and asexual reproduction.

Phases of Mitosis:

1. Interphase (not part of mitosis but prepares the cell):

   • G1 Phase: Cell growth and normal functions.

   • S Phase: DNA replication occurs.

   • G2 Phase: Further growth and preparation for division.

2. Prophase:

   • Chromosomes condense into visible structures.

   • The nuclear membrane begins to break down.

   • Spindle fibers begin to form.

3. Metaphase:

   • Chromosomes align at the cell's equator (metaphase plate).

   • Spindle fibers attach to the centromeres of chromosomes.

4. Anaphase:

   • Sister chromatids are pulled apart toward opposite poles of the cell.

5. Telophase:

   • Chromosomes begin to de-condense.

   • The nuclear membrane re-forms around each set of chromosomes.

6. Cytokinesis:

   • The cytoplasm divides, resulting in two daughter cells.

   • In animal cells, the membrane pinches to form two cells (cleavage furrow).

   • In plant cells, a new cell wall forms (cell plate).

3. Meiosis: Sexual Reproduction and Genetic Diversity

Meiosis is a type of cell division that reduces the chromosome number by half and produces four non-identical gametes (sperm or eggs).

Phases of Meiosis:

Meiosis I (Reduction Division):

1. Prophase I:

   • Homologous chromosomes pair up and form tetrads.

   • Crossing over (exchange of genetic material) occurs between homologous chromosomes, increasing genetic diversity.

   • The nuclear membrane breaks down.

2. Metaphase I:

   • Homologous chromosome pairs align at the metaphase plate.

3. Anaphase I:

   • Homologous chromosomes are pulled to opposite poles (reduction in chromosome number).

4. Telophase I and Cytokinesis:

   • The cell divides into two haploid cells (each with half the number of chromosomes).

Meiosis II (Equational Division):

• Similar to mitosis but with no DNA replication before the division.

1. Prophase II: Chromosomes condense.

2. Metaphase II: Chromosomes align at the metaphase plate.

3. Anaphase II: Sister chromatids are separated.

4. Telophase II and Cytokinesis: Four non-identical haploid cells are produced.

4. DNA: Structure and Function

DNA (deoxyribonucleic acid) carries the genetic instructions for life.

Structure of DNA:

• Double Helix: Two strands of nucleotides wound around each other.

• Nucleotides: Consist of a sugar (deoxyribose), a phosphate group, and a nitrogenous base.

  • Bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

  • A pairs with T, and C pairs with G.

DNA Replication:

• Unwinding: The double helix is unwound by the enzyme helicase.

• Base Pairing: DNA polymerase adds complementary nucleotides to the exposed strands.

• Result: Two identical DNA molecules, each with one old strand and one new strand (semiconservative replication).

Gene Expression:

• Transcription: The DNA sequence is copied into mRNA (messenger RNA).

• Translation: mRNA is translated into a protein by ribosomes in the cytoplasm.

1. What is Optics?

Optics is the branch of science that studies light and how it behaves when it interacts with different materials like mirrors, lenses, and other objects.

2. Light and its Properties

Light is a type of energy that travels in waves. It behaves like a wave and can travel through space (vacuum) and different materials.

• Wavelength: The distance between two peaks (crests) of a wave. It determines the color of light.

• Frequency: The number of waves that pass a point in one second. Higher frequency = more energy.

• Speed of Light: Light travels at a very fast speed—about 300,000 kilometers per second.

3. Geometrical Optics (How Light Travels)

In geometrical optics, we focus on the path that light travels along, which is called a ray.

Reflection (Bouncing Light)

• Reflection happens when light bounces off a surface like a mirror.

• Law of Reflection: The angle at which light hits the mirror (angle of incidence) is equal to the angle at which it bounces off (angle of reflection).

  • Formula: Angle of incidence=Angle of reflectionAngle of incidence=Angle of reflection

Refraction (Bending Light)

• Refraction occurs when light passes from one material to another (like from air into water) and bends.

• Example: A straw in a glass of water looks broken or bent due to refraction.

Refractive Index (n)

• The refractive index of a material tells us how much light slows down when it enters that material.

  • Air has a refractive index of 1, and water has a refractive index of about 1.33, meaning light slows down more in water.

4. Mirrors

Mirrors reflect light to form images. There are different types of mirrors, and they can form different kinds of images.

Types of Mirrors:

• Concave Mirror (Curved Inward): It can form real or virtual images depending on the distance from the object.

• Convex Mirror (Curved Outward): Always forms virtual, upright, and smaller images.

5. Lenses

Lenses bend light in different ways. There are two main types of lenses:

• Convex Lenses (Converging Lenses): These are thicker in the middle and bend light toward a point. They can form real or virtual images.

• Concave Lenses (Diverging Lenses): These are thinner in the middle and spread light out. They always form virtual, smaller images.

7. Dispersion and Color

• Dispersion occurs when light separates into different colors. For example, when light passes through a prism, it bends and spreads into a rainbow of colors (red, orange, yellow, green, blue, indigo, violet).

• This happens because different colors (wavelengths) of light bend by different amounts. Red light bends the least, and violet light bends the most.

1. What is Electricity?

Electricity is a form of energy caused by the movement of electrons through a material. It powers most of the devices and technology we use every day.

Key Concepts:

• Electric Current (I): The flow of electric charge (usually electrons) through a conductor. Measured in amperes (A).

• Voltage (V): The electric potential difference between two points. It’s what pushes the electric charge to move. Measured in volts (V).

• Resistance (R): The opposition to the flow of electric current. Measured in ohms (Ω).

2. Ohm's Law

Ohm's Law relates the voltage, current, and resistance in an electrical circuit. It’s one of the most important laws in electricity.

• Formula: V=I×RV=I×R

  • VV = Voltage (volts, V)

  • II = Current (amperes, A)

  • RR = Resistance (ohms, Ω)

• Rearranged formulas:

  • To find current: I=VRI=RV​

  • To find resistance: R=VIR=IV​

Example:
If a circuit has a voltage of 12V and a resistance of 6Ω, the current would be:
I=VR=12V6Ω=2AI=RV​=6Ω12V​=2A

3. Types of Circuits

There are two main types of electrical circuits: series circuits and parallel circuits.

Series Circuit:

• In a series circuit, all components are connected end-to-end in a single path.

• Current is the same through all components.

• Voltage is divided between the components.

• Total Resistance in a series circuit is the sum of the individual resistances:

  • Formula: Rtotal=R1+R2+R3+…Rtotal​=R1​+R2​+R3​+…

Example:
If three resistors of 2Ω, 3Ω, and 5Ω are connected in series, the total resistance is:
Rtotal=2Ω+3Ω+5Ω=10ΩRtotal​=2Ω+3Ω+5Ω=10Ω

Parallel Circuit:

• In a parallel circuit, components are connected across common points, creating multiple paths for the current.

• Voltage is the same across all components.

• Current is divided among the different paths.

• Total Resistance in a parallel circuit is calculated using the formula:

  • Formula: 1Rtotal=1R1+1R2+1R3+…Rtotal​1​=R1​1​+R2​1​+R3​1​+…

Example:
If three resistors of 2Ω, 3Ω, and 6Ω are connected in parallel, the total resistance is:
1Rtotal=12Ω+13Ω+16Ω=1ΩRtotal​1​=2Ω1​+3Ω1​+6Ω1​=1Ω

4. Power in Circuits

The power (P) used by an electrical device is the rate at which electrical energy is converted into another form of energy (like heat, light, or motion).

• Formula: P=V×IP=V×I

  • Where:

    • P = Power (watts, W)

    • V = Voltage (volts, V)

    • I = Current (amperes, A)

• You can also use Ohm's Law to find power in terms of resistance:

  • Formula: P=I2×RP=I2×R or P=V2RP=RV2​

Example:
If a circuit has a voltage of 10V and a current of 2A, the power is:
P=10V×2A=20WP=10V×2A=20W

5. Conductors and Insulators

• Conductors: Materials that allow electric charge to flow easily (e.g., metals like copper and aluminum).

• Insulators: Materials that do not allow electricity to flow through them easily (e.g., rubber, plastic, wood).

6. Measuring Electric Current and Voltage

• Ammeter: A device used to measure the current in a circuit. It must be connected in series with the components.

• Voltmeter: A device used to measure the voltage across two points. It must be connected in parallel with the components.

7. Electrical Safety

• Always handle electrical devices with dry hands and keep them away from water.

• Use insulated wires and electrical appliances that are properly grounded.

• Never overload circuits, as this can cause short circuits or fires.

8. Key Formulas Summary

1. Ohm’s Law:
   V=I×RV=I×R

2. Power:
   P=V×IP=V×I
   or
   P=I2×RP=I2×R
   or
   P=V2RP=RV2​

3. Total Resistance in Series:
   Rtotal=R1+R2+R3+…Rtotal​=R1​+R2​+R3​+…

4. Total Resistance in Parallel:
   1Rtotal=1R1+1R2+1R3+…Rtotal​1​=R1​1​+R2​1​+R3​1​+…

10. Quick Recap

• Electricity is the flow of electrons through a conductor.

• Current (I) flows from high to low potential (positive to negative).

• Voltage (V) pushes the current through a circuit.

• Resistance (R) opposes the flow of current.

• Ohm’s Law is the relationship between voltage, current, and resistance: V=I×RV=I×R.

• In series circuits, current stays the same, but voltage divides; in parallel circuits, voltage stays the same, but current divides

1. Sexual Reproduction

Sexual reproduction is a process where two parents (usually one male and one female) contribute genetic material(gametes) to produce offspring that are genetically different from the parents.

Key Concepts:

• Gametes: Reproductive cells that carry half the genetic material of an individual. These are:

  • Sperm (male gametes)

  • Egg (female gametes)

• Fertilization: The process where a sperm cell meets and joins with an egg cell to form a zygote. The zygote then divides and grows into an embryo.

• Genetic Diversity: Sexual reproduction allows for mixing of genes from both parents, leading to offspring with unique genetic combinations. This is important for evolution and adaptation to environmental changes.

• Chromosomes: Gametes have half the number of chromosomes as the parent cells. When fertilization happens, the number of chromosomes in the zygote is restored to the full number (diploid).

  • Example: In humans, each parent contributes 23 chromosomes, making a total of 46 chromosomes in the zygote.

Advantages of Sexual Reproduction:

• Genetic Variation: Offspring inherit different combinations of genes from both parents, making them more likely to adapt to changing environments.

• Survival: The genetic variation helps populations survive diseases, environmental changes, and other challenges.

Disadvantages of Sexual Reproduction:

• Energy and Time: It takes time and energy to find a mate, produce gametes, and care for offspring.

• Fewer Offspring: Sexual reproduction typically produces fewer offspring compared to asexual reproduction.

2. Asexual Reproduction

Asexual reproduction is a process where a single parent produces offspring that are genetically identical to itself. There is no fusion of gametes.

Key Concepts:

• Binary Fission: In organisms like bacteria, the parent cell divides into two identical daughter cells. This is the most common form of asexual reproduction in single-celled organisms.

• Budding: In organisms like yeast and hydra, a new organism grows from a small outgrowth (bud) on the parent’s body. The bud eventually breaks off and develops into a new organism.

• Fragmentation: In some animals like starfish, if a part of the body (such as an arm) breaks off, it can grow into a new individual.

• Vegetative Propagation: Plants can reproduce asexually through structures like runners (e.g., strawberries), tubers (e.g., potatoes), and cuttings (e.g., plants like geraniums).

Advantages of Asexual Reproduction:

• Speed and Efficiency: Since only one parent is involved, it is quicker and requires less energy to produce offspring. Many offspring can be produced in a short period of time.

• No Mate Required: Organisms don’t need to find a mate, which is helpful in environments where mates are scarce.

Disadvantages of Asexual Reproduction:

• No Genetic Variation: All offspring are genetically identical (clones). This can be a disadvantage in changing environments because there is little adaptability.

• Vulnerability: A single disease or environmental change could wipe out an entire population since all individuals are genetically the same.

3. Requirements of a Living Organism

For something to be considered alive, it must meet certain characteristics or requirements. These are often referred to as the 7 characteristics of living organisms.

Key Requirements:

1. Movement:

   • Living organisms can move in some way, either actively (e.g., animals walking, plants growing towards light) or passively (e.g., wind moving seeds).

2. Respiration:

   • Living organisms need to get energy by breaking down food. This can be through aerobic respiration (using oxygen) or anaerobic respiration (without oxygen).

   • Plants also perform photosynthesis, which is a way of making food using sunlight, water, and carbon dioxide.

3. Sensitivity:

   • Organisms can sense and respond to changes in their environment (e.g., plants grow towards light, animals move away from danger).

4. Growth:

   • Living organisms grow and develop over time. This can involve increasing in size (e.g., animals growing) or more complex changes like developing different stages (e.g., caterpillar to butterfly).

5. Reproduction:

   • All living organisms must be able to reproduce to pass on their genes and continue their species. This can be done sexually or asexually.

6. Excretion:

   • Organisms need to get rid of waste products produced by metabolism (e.g., animals excrete urine, plants excrete oxygen as a waste product of photosynthesis).

7. Nutrition:

   • All living organisms need a source of nutrients to survive. This can come from eating other organisms (consumers), making their own food (producers like plants), or breaking down dead organisms (decomposers like fungi).

Summary of Key Differences Between Sexual and Asexual Reproduction:

1. Bohr Models (Atomic Structure)

• What is a Bohr Model?

  • A Bohr model shows how the electrons of an atom are arranged around the nucleus (the center of the atom).

  • Nucleus: The nucleus is made up of protons and neutrons. Protons have a positive charge and neutrons have no charge.

  • Electrons: Electrons are much smaller than protons and neutrons and have a negative charge. They move around the nucleus in energy levels or shells.

• Key Points:

  • The first shell can hold 2 electrons.

  • The second shell can hold 8 electrons.

  • The third shell can hold 18 electrons, but it fills with 8 electrons first before moving to the next shell.

• Example: Carbon (C) (Atomic Number = 6)

  • Bohr Model for Carbon:

    • Nucleus: 6 protons, 6 neutrons.

    • First shell: 2 electrons.

    • Second shell: 4 electrons.

2. Calculating Mass, Density, and Volume

• Mass: The amount of matter in an object. It's usually measured in grams (g) or kilograms (kg).

• Density: How much mass is in a certain volume of a substance. The formula for density is:

  Density=MassVolumeDensity=VolumeMass​

  • Units for density are typically g/cm³ (grams per cubic centimeter) or kg/m³ (kilograms per cubic meter).

• Volume: The amount of space an object takes up. Volume is measured in cubic centimeters (cm³) or liters (L).

  • For a regular-shaped object (like a box or a cube), you calculate the volume by:

  Volume=Length×Width×HeightVolume=Length×Width×Height

  • For irregular objects, you can measure the volume by water displacement. This means placing the object in water and measuring the rise in water level.

Example:

• Find the density of an object with a mass of 10 grams and a volume of 5 cm³:Density=10 g5 cm3=2 g/cm3Density=5cm310g​=2g/cm3

3. The Periodic Table

• The Periodic Table organizes all known elements based on their atomic number (number of protons). It is divided into rows (called periods) and columns (called groups or families).

• Groups: Elements in the same column (group) have similar chemical properties. For example:

  • Group 1: Alkali metals (e.g., lithium, sodium) are very reactive, especially with water.

  • Group 18: Noble gases (e.g., helium, neon) are non-reactive because their electron shells are full.

• Periods: Each row in the periodic table represents elements with the same number of electron shells.

• Examples:

  • Hydrogen (H): Atomic number 1, 1 proton, 1 electron.

  • Oxygen (O): Atomic number 8, 8 protons, 8 electrons.

  • Sodium (Na): Atomic number 11, 11 protons, 11 electrons.

4. Particle Model of Matter

• Basic Idea: Matter is made up of tiny particles (atoms or molecules) that are always in motion. These particles are too small to see with the naked eye.

• Three States of Matter:

  • Solid: Particles are packed tightly together and vibrate in place. Solids have a definite shape and definite volume.

  • Liquid: Particles are still close together but can move past each other. Liquids have a definite volume, but their shape can change to fit the container.

  • Gas: Particles are far apart and move freely. Gases have no definite shape or definite volume. They expand to fill whatever space they are in.

• Temperature and Particle Motion:

  • Hotter substances: Particles move faster.

  • Colder substances: Particles move slower.

5. Kinetic Molecular Theory (KMT)

• KMT explains how the particles of matter behave:

  1. All matter is made up of tiny particles (atoms or molecules).

  2. These particles are in constant motion, and the more energy they have, the faster they move.

  3. Gases: The particles in a gas move the fastest and are far apart from each other.

  4. Solids: Particles are tightly packed and vibrate in place (they don’t move past each other).

  5. The temperature of a substance is related to the average speed of the particles. Higher temperature = faster movement.

6. States of Matter

• Solid:

  • Particles are close together and vibrate in place.

  • Definite shape and definite volume.

  • Example: Ice, wood, metal.

• Liquid:

  • Particles are close together but can move past each other.

  • Definite volume but no definite shape (takes the shape of the container).

  • Example: Water, juice, oil.

• Gas:

  • Particles are far apart and move freely.

  • No definite shape or definite volume (expands to fill the container).

  • Example: Air, oxygen, carbon dioxide.

• Plasma:

  • An ionized state of matter, consisting of charged particles.

  • Found in stars and lightning.

  • Example: Sun, neon signs.

7. Quarks

• Quarks are the tiny building blocks that make up protons and neutrons. Quarks are elementary particles, which means they are not made up of anything smaller.

• Types of Quarks:

  • Up quark (u): Has a charge of +2/3.

  • Down quark (d): Has a charge of -1/3.

• Protons are made of two up quarks and one down quark: (uud).

• Neutrons are made of two down quarks and one up quark: (udd).

• Quarks are held together inside protons and neutrons by strong forces, carried by particles called gluons.

8. Leptons

• Leptons are a type of elementary particle that don’t interact via the strong force.

  • Electron: The most common lepton, found in atoms.

  • Muon: Similar to an electron but much heavier.

  • Tau: Even heavier than the muon.

  • Neutrinos: Very light and don’t interact much with matter.

• Important Leptons:

  • Electron (e−e−): Negative charge, found around the nucleus of atoms.

  • Neutrino: Very small, neutral, and almost massless.

Key Formulas to Remember:

• Density:Density=MassVolumeDensity=VolumeMass​

• Mass:Mass=Density×VolumeMass=Density×Volume

• Volume:Volume=MassDensityVolume=DensityMass​