B1 Biology: Cells, Body Systems, and Reproduction Flashcards

Learning Objectives for Topic 1.1: Observing Cells

Define what a cell is.
Describe how to use a microscope to observe very small objects.
Calculate the total magnification used to observe an object.

Understanding Cells and Organisms

Biological Definition of Cells: All living things, formally referred to as organisms, are composed of cells. Cells are categorized as the fundamental building blocks of life and represent the smallest units found within an organism.
Organisational Scale:
- Unicellular Organisms: Some organisms, such as bacteria, are comprised of only a single cell.
- Multicellular Organisms: Larger organisms, including humans, are composed of millions of cells joined together.
Historical Context: Cells were first observed approximately $350$ years ago by the scientist Robert Hooke. Using a microscope to examine a thin slice of cork (tree bark), he identified tiny room-like structures and coined the term 'cells'.

Microscope Techniques and Observations

Making an Observation: An observation in biology refers to looking carefully and in detail at an object. This is facilitated by a microscope, which magnifies images using lenses.
Specimen Preparation: To allow light to travel through the object for visibility, the specimen must be very thin. Coloured dyes are often added to specimens to enhance visibility, such as in the observation of different types of blood cells.
Standard Parts of a Light Microscope:
- Eyepiece: The lens the observer looks through.
- Objective Lens: The lens situated closest to the specimen; multiple lenses of different magnifications are typically available.
- Stage: The platform where the slide is placed.
- Slide: The thin piece of glass containing the specimen.
- Coarse-Focus Knob: Used for initial, large-scale focusing.
- Fine-Focus Knob: Used for precision focusing to bring the image into clear view.
- Light: Illuminates the specimen from below.

Step-by-Step Procedure for Microscope Use

Lower the Stage: Move the microscope stage to its lowest position.
Mount the Specimen: Place the object to be observed (on a slide) onto the stage.
Initial Lens Selection: Select the objective lens with the lowest magnification power.
Initial Focus: Look through the eyepiece and slowly rotate the coarse-focus knob until the object is visible.
Refine Focus: Adjust the fine-focus knob until the object appears in sharp focus.
Increase Detail: Repeat the process using objective lenses of higher magnification to observe the specimen in greater detail.

Mathematical Application: Magnification Formula

Total magnification is the product of the eyepiece lens magnification and the objective lens magnification.
Formula: $\text{Total Magnification} = \text{Eyepiece Lens Magnification} \times \text{Objective Lens Magnification}$
Example Calculation: If the eyepiece lens is $\times 10$ and the objective lens is $\times 4$ , the calculation is $10 \times 4 = 40$ . The object appears $40$ times larger than its actual size.
Self-Test Example: Using an onion cell with a $\times 10$ eyepiece and a $\times 40$ objective, the total magnification is $10 \times 40 = 400$ .

Plant and Animal Cells: Structural Comparison

General Components: Both plant and animal cells contain smaller parts called components or organelles, each with specific metabolic functions. Animal cells typically exhibit an irregular shape, while plant cells have a regular, brick-like structure.
Shared Components (Found in both Animal and Plant Cells):
- Nucleus: Controls the cell's activities and contains genetic material (DNA), which is essential for creating new cells.
- Cell Membrane: A biological barrier surrounding the cell that regulates the entry and exit of substances.
- Cytoplasm: A 'jelly-like' substance where the majority of chemical reactions occur.
- Mitochondria: The site of aerobic respiration, a chemical reaction that transfers energy for the organism.
Components Unique to Plant Cells:
- Cell Wall: Made of a tough fibre called cellulose, this rigid structure strengthens the cell and provides physical support.
- Vacuole: Contains a watery liquid called cell sap; it maintains internal pressure to keep the cell firm.
- Chloroplasts: The site of photosynthesis. These contain chlorophyll, a green pigment that traps solar energy. (Note: Root cells do not contain chloroplasts as they are underground and lack access to light).
Etymology Note: The prefix 'chloro' means 'green', as seen in chlorophyll and chloroplast.

Specialized Cells and Adaptations

Definition: Specialised cells possess specific shapes and structures (adaptations) that allow them to perform particular physiological functions.
Animal Cell Specialisations:
- Nerve Cells (Neurones): Long and thin with branched connections at each end to transmit electrical impulses throughout the body.
- Red Blood Cells: Transport oxygen. They contain haemoglobin (red pigment), lack a nucleus to save space, and have a biconcave disc shape to increase surface area for oxygen absorption.
- Sperm Cells: Carry male genetic material. Adaptations include a streamlined head, a long tail for swimming, and high densities of mitochondria to provide the energy required for movement.
- Egg Cells: Contain fat stores in the cytoplasm for nourishment; surrounded by a jelly layer to protect the cell and attract sperm.
Plant Cell Specialisations:
- Leaf Cells (Palisade Cells): Located on the upper surface of leaves. They are long, thin, and packed with chloroplasts to maximize light absorption for photosynthesis.
- Root Hair Cells: Absorb water and nutrients from soil. They feature long 'hairs' to create a massive surface area. They lack chloroplasts because photosynthesis cannot occur underground.

Movement of Substances: Diffusion

Defining Diffusion: Diffusion is the passive movement of particles from an area of high concentration to an area of low concentration until equilibrium is reached.
Concentration: Refers to the number of particles of a substance present in a specific volume or space.
Biological Utility:
- Nutrient Intake: Glucose and oxygen diffuse from the blood into cells for respiration.
- Waste Removal: Carbon dioxide, a waste product of respiration, diffuses out of cells into the blood to be transported to the lungs for excretion.
- Plant Physiology: Water enters plants via diffusion into root hair cells (from high water concentration in soil to low concentration in the cell). Oxygen and carbon dioxide diffuse into and out of leaves via tiny pores.
Plant Wilting: When a plant lacks water, the vacuole in its cells shrinks. This reduces the outward pressure on the cell wall, causing the cells to become floppy and the plant to wilt.

Unicellular Organisms

Definition: Organisms comprised of exactly one cell. They are distinct from the plant and animal kingdoms.
Amoeba:
- Characteristics: No fixed shape (blob-like); found in fresh water, salt water, and soil.
- Form: Membrane-bound cytoplasm with a nucleus.
- Movement: They change shape by extending parts of their body and letting the rest follow.
- Nutrition: They 'engulf' food (algae, bacteria) by surrounding it to form a food vacuole for digestion. Waste is managed by a contractile vacuole to prevent bursting.
- Reproduction: They reproduce via binary fission (splitting into two identical daughter cells).
Euglena:
- Characteristics: Microscopic, found in fresh water. Contain a nucleus, cytoplasm, and contractile vacuole.
- Plant-like traits: Contain chloroplasts for photosynthesis when light is available.
- Animal-like traits: Can engulf food (bacteria/algae) when light is scarce. Possess an eye spot to detect light and a flagellum (tail-like structure) used for swimming toward light.

Human Gas Exchange and Respiratory System

Gas Exchange: The transfer of gases (oxygen in, carbon dioxide out) between an organism and its environment. It occurs in the lungs.
Anatomy of the Respiratory System:
- Pathway: Nose/Mouth $\rightarrow$ Trachea (windpipe) $\rightarrow$ Bronchus $\rightarrow$ Bronchiole $\rightarrow$ Alveolus (air sac).
- Alveoli Adaptations: Specialized for rapid gas exchange with thin walls (one cell thick) and a large total surface area.
Air Composition Comparison:
- Inhaled Air: Oxygen ( $20.96\%$ ), Carbon Dioxide ( $0.04\%$ ), Nitrogen ( $79\%$ ).
- Exhaled Air: Oxygen ( $16\%$ ), Carbon Dioxide ( $5\%$ ), Nitrogen ( $79\%$ ). Contains more water vapour (a waste product of respiration) and is warmer.

The Mechanics of Breathing

Inhalation (Breathing In):
- Intercostal muscles contract, pulling the ribcage up and out.
- The diaphragm contracts and moves downward.
- Internal chest volume increases; chest pressure decreases, drawing air into the lungs.
Exhalation (Breathing Out):
- Intercostal muscles relax, pulling the ribcage down and in.
- The diaphragm relaxes and moves upward.
- Internal chest volume decreases; chest pressure increases, pushing air out.
Measuring Lung Volume: Can be estimated by blowing into a water-filled container and measuring the displaced volume. Exercise can increase lung volume, while asthma, smoking, and aging can decrease it.

The Human Skeleton

Composition: The average adult human skeleton consists of $206$ bones. Bone is a living tissue with its own blood supply, capable of growth and self-repair.
Functions of the Skeleton:
1. Support: Provides a framework that holds organs in place and keeps the body upright (especially the vertebral column/backbone).
2. Protection: Hard bones shield vital organs (e.g., skull protects the brain, ribcage protects the heart and lungs).
3. Movement: Provides a structure for muscles to pull against.
4. Blood Cell Production: Long bones contain bone marrow, which produces red blood cells (for oxygen) and white blood cells (for infection protection).

Joints and Biomechanics

Biomechanics: The study of how muscles and joints work together to produce movement.
Types of Joints:
- Hinge Joint: Backwards and forwards movement (e.g., knee, elbow).
- Ball-and-Socket Joint: Movement in all directions (e.g., hip, shoulder).
- Pivot Joint: Rotation around a point (e.g., neck).
- Fixed Joint: No movement allowed (e.g., skull).
Joint Structure: Bones are held together by ligaments. To prevent wearing down through friction, bone ends are covered in smooth cartilage and kept slippery by joint fluid.
Muscle Strength: Measured in Newtons ( $N$ ) using a newton scale. Arm muscles are significantly stronger than facial muscles.

Muscle Function and Antagonistic Pairs

Movement Mechanism: Muscles cause movement by contracting (shortening). They are attached to bones by tendons. Muscles can only pull; they cannot push.
Antagonistic Muscles: Pairs of muscles that work in opposition to control movement at a joint. When one contracts, the other relaxes.
Example: Biceps and Triceps:
- To bend the arm: Biceps contracts, Triceps relaxes.
- To straighten the arm: Triceps contracts, Biceps relaxes.

Human Reproduction and Development

Adolescence: The transitional period between childhood and adulthood involving emotional and physical changes.
Puberty: The physical changes that occur during adolescence (typically ages $9$ - $14$ ), triggered by sex hormones.
- Shared Changes: Pubic/underarm hair growth, body odour, growth spurts.
- Female Specific: Breast development, hip widening, onset of periods (menstruation).
- Male Specific: Voice breaks, testes/penis enlargement, sperm production, shoulder widening, facial hair.
Anatomy:
- Male: Testes (produce sperm/hormones), Scrotum (holds testes), Semen (mixture of sperm and fluid), Sperm Ducts, Urethra, Penis.
- Female: Ovaries (contain egg cells), Oviducts (egg tubes with cilia), Uterus (womb), Cervix (muscle ring), Vagina.
Gestation (Pregnancy): Lasts approximately $9$ months or $40$ weeks in humans. The embryo becomes a foetus after $8$ weeks. The placenta allows for nutrient/oxygen/waste exchange without mixing maternal and foetal blood.
The Menstrual Cycle: A cycle lasting approximately $28$ days. Ovulation (egg release) typically occurs on Day $14$ . If not fertilised, the uterus lining sheds (Period).
Contraception: Methods to prevent pregnancy. Condoms act as a barrier and prevent STIs ( $98\%$ effective if used correctly). The contraceptive pill prevents ovulation via hormones.

Plant Reproduction and Life Cycle

Flower Anatomy:
- Stamen (Male): Anther (pollen production) and Filament.
- Carpel (Female): Stigma (sticky to catch pollen), Style, and Ovary (contains ovules).
Pollination: The transfer of pollen from anther to stigma. Can be self-pollination or cross-pollination. Methods include wind (light, abundant pollen) and insects (bright petals, nectar, sticky pollen).
Fertilisation and Germination: After pollination, a pollen tube grows down the style. The pollen nucleus joins with the ovule nucleus. The ovary becomes the fruit; ovules become seeds.
Requirements for Germination: Water (to swell/split coat), Oxygen (for respiration energy), and Warmth (to speed reactions).
Seed Dispersal: Moving seeds away from the parent plant to reduce competition for light and nutrients. Methods include: Wind (parachutes/wings), Animals (Internal: fruit consumption; External: hooks/fur), Water (floating/waterproof), and Explosive (bursting pods).

Questions & Discussion

Question: What equipment can you use to look at small objects in detail?
Response: Hand lens, magnifying glass, or microscope.
Question: What are the main structures in a plant?
Response: Roots, stem, leaf, and flower.
Question: Name some organs found in the human body.
Response: Heart, lungs, stomach, and eyes.
Question: State why coloured dye might be added to a specimen before observation.
Response: To make the object or specific components inside it easier to see by providing contrast.
Question: Why do bus windows steam up on cold days?
Response: Warm, exhaled air contains water vapour (a waste product of respiration). When it hits the cold glass, it condenses into liquid droplets.