Grade 8 Curiosity - Chapter 2: Cell - The Building Block of Life

Flashcards covering the fundamentals of cell biology, microscopy, organelle function, and the origins of life based on the provided lecture transcript.

It is widely accepted that life originated in water, potentially in small water pools or ________.

hot springs

The hot springs of ________ in Ladakh maintain temperatures nearly at the boiling point of water.

Puga Valley

Environmental conditions in Puga Valley are similar to early Earth about ________ billion years ago.

$$3.5$$

Heat-loving bacteria found in hot springs are called ________.

thermophiles

Scientists from the ________ Institute of Palaeosciences, Lucknow, studied hot springs for evidence of early life.

Birbal Sahni

Deposits of ________ formed rapidly around hot springs might have protected early organic molecules.

calcium carbonate

Calcium carbonate deposits may have helped in the formation of the first ________, which defines a cell.

protective membrane

The ________ represents the basic level at which life exists.

cell

Organisms like bacteria or yeast that consist of only one cell are described as ________.

unicellular

Humans and plants are ________ organisms because they are made up of millions of cells.

multicellular

A group of similar cells performing similar functions forms ________.

tissues

Different tissues are organized to form an ________.

organ

Several organs work together to form ________.

organ systems

The nasal cavity, trachea, and lungs form the ________ system.

respiratory

Even within organ systems, the cell remains the fundamental unit of ________ and ________.

structure; function

The ability of the human eye to see two close objects as distinct is the ________.

limit of resolution

At a near point of $25\,\text{cm}$, the resolution of the human eye is about ________.

$$0.1\,\text{mm}$$

A ________ lens or a combination of lenses is used for the magnification of objects.

convex

In 1665, ________ was the first person to observe a cell.

Robert Hooke

Robert Hooke reached a magnification of about ________ using a self-designed microscope.

$$200–300X$$

Hooke observed small box-like compartments in a thin slice of ________.

cork

Modern school laboratories use ________ microscopes under visible light.

light

$1\,\text{millimetre (mm)}$ is equal to ________ micrometres ($\mu\text{m}$).

$$1000$$

Estimated size of a cell is the diameter of the visible field divided by the ________ along the diameter.

number of cells

If the diameter is $5000\,\mu\text{m}$ and $25$ cells are counted, the size of one cell is ________.

$$200\,\mu\text{m}$$

Total magnification is the product of the magnifying power of the ________ and the eyepiece.

objective lens

If the eyepiece is $10X$ and the objective is $10X$, the total magnification is ________.

$$100X$$

Microscope improvements focus on three features: resolution, magnification, and ________.

contrast

Contrast refers to the difference in ________ between various parts of an object.

brightness

A ________ uses a beam of electrons to see cell structures at the nanometre scale.

powerful electron microscope

A nanometre is ________ of a metre.

one-billionth

The lower surface of a ________ leaf can be observed under a Scanning Electron Microscope.

Colocasia

The ________ is the thin boundary that surrounds and protects cell contents.

cell membrane

Another name for the cell membrane is the ________ membrane.

plasma

The cell membrane is ________, meaning it allows only some substances to pass.

selectively permeable

Particles of matter intermix due to a difference in concentrations called a ________.

concentration gradient

________ is the net movement of particles from a higher to a lower concentration.

Diffusion

________ is specifically defined as the diffusion of water across a selectively permeable membrane.

Osmosis

In Beaker B, a potato piece in $20$ per cent salt solution will ________.

shrink

Water moves from an area with ________ solute to an area with ________ solute during osmosis.

less; more

Wait until ________ in two areas become equal during the osmosis process.

concentrations

A solution where the extracellular solute concentration equals the intracellular concentration is ________.

isotonic

In a ________ solution, the external solute concentration is lower than the internal concentration.

hypotonic

In a ________ solution, the external solute concentration is higher than the internal concentration.

hypertonic

Structurally, the cell membrane is about ________ thick.

$$7\,\text{to}\,10\,\text{nanometres (nm)}$$

$1$ nanometre is equal to ________ $mm$.

$$0.000001$$

The cell membrane is primarily made up of ________ and proteins.

lipids (fats)

The ________ model explains that molecules in the membrane can move sideways and flip.

fluid-mosaic

The membrane has a ________ bilayer with water-attracting heads and repelling tails.

lipid

Proteins embedded in the membrane act like ________ for passing substances.

gatekeepers

Plant, fungi, and bacteria cells have an additional outer layer called the ________.

cell wall

Plant cells are box-shaped, while ________ cells are irregularly arranged.

human cheek

To observe plant cells under a microscope, safranin is used for mounting a thin peel of ________.

onion leaf

________ stain is added to human cheek cells for microscopic observation.

methylene blue

In a concentrated sugar solution, the plant cell membrane pulls away from the wall, a state called ________.

shrinkage

The ________ provides a rigid structure that helps plants withstand wind and rain.

cell wall

Though rigid, the cell wall is ________, allowing water and minerals to pass.

permeable

The plant cell wall is primarily made of ________, a type of carbohydrate.

cellulose

Cellulose consists of many units of ________ linked together.

glucose

The cellular ________ of animal cells allows them to change shape easily.

flexibility

Apart from the membrane, most cells have a jelly-like ________ and a nucleus.

cytoplasm

A ________ cell lacks a well-defined nucleus and membrane-bound organelles.

prokaryotic

In terms of nomenclature, "pro" means ________ and "karyon" means nucleus.

primitive

Cells with a well-defined nucleus and membrane-bound organelles are called ________.

eukaryotic

The diameter of a typical prokaryotic cell is ________.

$$1\,\text{to}\,10\,\mu\text{m}$$

The diameter of a typical eukaryotic cell is ________.

$$10\,\text{to}\,100\,\mu\text{m}$$

Prokaryotic organisms are usually ________.

unicellular

A network of fine fibres called the ________ provides structural support in eukaryotic cells.

cytoskeleton

Cell ________ are stored substances like starch, calcium oxalate, or silica in some cells.

inclusions

________ are acellular infectious agents composed of genetic material and a protein coat.

Viruses

________ lack a protein coat around their genetic material, unlike viruses.

Viroids

________ are misfolded proteins that lack genetic material.

prions

The double-layered covering of the nucleus is called the ________.

nuclear membrane

Material is transferred between the nucleus and cytoplasm through ________.

nuclear pores

The synthesis of ribosomal subunits takes place in the ________.

nucleolus

Information for inheritance is contained in rod-shaped structures called ________.

chromosomes

Rod-shaped chromosomes are only visible when the cell is ________.

about to divide

DNA stands for ________.

Deoxyribonucleic acid

The functional segments of DNA are called ________.

genes

In a non-dividing cell, DNA is present as an entangled mass of thread-like ________.

chromatin material

Mature human Red Blood Cells (RBCs) do not have a nucleus and are called ________.

enucleate

Human Red Blood Cells survive for approximately ________ days.

$$120$$

In prokaryotes, the region containing the circular DNA molecule is called the ________.

nucleoid

________ are the sites of protein synthesis in the cell.

Ribosomes

The ________ spreads like a network within the cytoplasm and is continuous with the nuclear envelope.

Endoplasmic Reticulum (ER)

________ looks rough because it has ribosomes attached to its surface.

Rough Endoplasmic Reticulum (RER)

Smooth Endoplasmic Reticulum (SER) is involved in the synthesis and storage of ________ and hormones.

fats (lipids)

The ________ apparatus was first observed in 1898 by Camillo Golgi in barn owl nerve cells.

Golgi

The Golgi apparatus modifies and packages proteins into ________ for transport.

vesicles

________ are single membrane-bound sacs filled with enzymes to digest waste.

Lysosomes

The ________ are called the 'powerhouses of the cell'.

Mitochondria

The inner membrane of a mitochondrion is folded into ________ to increase surface area.

cristae

The molecule ________ acts as the energy currency for cellular activities.

Adenosine Triphosphate (ATP)

Plants use special organelles called ________ for food synthesis and storage.

plastids

A green pigment called ________ is present in chloroplasts to absorb sunlight.

chlorophyll

Inside the chloroplast, the semi-fluid substance is called the ________.

stroma

Disc-shaped membrane structures within the stroma contain ________.

chlorophyll

Mitochondria and ________ both contain their own DNA and ribosomes.

chloroplasts

Energy released during cellular respiration is stored in ________ molecules.

ATP

Human sperm cells use ________ enzymes to break down the outer layer of the egg.

lysosomal