Cell Division

Stages of the cell cycle

Interphase (G1, S, G2) Mitosis (PMAT), Cytokinesis

Stages of interphase

G1, S, G2

what happens during G1 of interphase

proteins made and organelles duplicated

what happens during S-phase of interphase

DNA replication

what happens during G2 of interphase

Cell growth until it becomes large enough for division, synthesis of special proteins for mitosis

Name the 3 checkpoints in cell cycle

G1 checkpoint, G2 checkpoint, Metaphase checkpoint

what does the G1 checkpoint check for

DNA damage

What happens if the cell doesn’t meet requirements of G1 checkpoint

Cell enters resting state called G0

What does the G2 checkpoint check for

Cell has replicated DNA without error and has grown large enough to divide

What does metaphase checkpoint check for

That all chromosomes are attached to spindles and are aligned

What happens during the prophase of mitosis

• chromatin fibres condense to form chromosomes

• nuclear envelope breaks down

• centrioles halve and move to poles

• centrioles form spindle threads

What happens during the metaphase of mitosis

• chromosomes move to central region of spindle

• chromosomes attach to spindle thread by centromere

What happens during the anaphase of mitosis

spindle fibres shorten and pull sister chromatids apart towards poles

What happens during the telophase of mitosis

• chromatids reach opposite poles, the uncoil to become long and thin again

• spindle breaks down and dissapears

• nuclear envelope forms around each set of genetic material

What happens during cytokinesis

Cell splits into 2, creating 2 daughter cells that are genetically identical to parent cell and one another

Prophase

Metaphase

Anaphase

Telophase

Cytokinesis

What is the significance of meiosis?

Gamete cells only need one chromosome from each pair during sexual reproduction

Are gametes haploid or diploid cells?

Haploid

What is meant by homologous pair of chromosomes

Have the same genes at the same locations

What is the difference between mitosis and meiosis 1?

Mitosis: sister chromatids are pulled apart, so end up with one chromosome from each pair in either new cell

Meiosis 1: homologous chromosomes are separated

What type of cells are created after meiosis I?

Haploid cells

What type of cells are created after meiosis II?

Haploid cells

What is crossing over?

Non-sister chromatids exchange alleles

What stage of meiosis does crossing over occur in?

Prophase

What two processes ensure genetic variation during meiosis?

Independent assortment, crossing over

What is independent assortment?

Random alignment of homologous pairs along the equator of the spindle

What is a bivalent?

When homologous chromosomes pair up

Compare anaphase I and II in meiosis

Anaphase II homologous pairs are pulled apart whereas anaphase I sister chromatids are pulled apart

What is a chromosome?

A thread-like structure containing nucleic acids that carries genetic information as genes

What is the point at which crossing over occurs called?

Chiasma

What is a chromosome made up of in meiosis I?

2 sister chromatids joined together by a centromere

How are chromosomes arranged in meiosis I?

Side by side, in homologous pairs (called bivalents)

How are homologous pairs of chromosomes pulled apart in meiosis I?

During anaphase I, microtubules pull whole chromosomes to opposite ends

Why is there not an interphase between meiosis I and II?

The DNA is not replicated

Erythrocyte function

Transport oxygen around the body

Erythrocyte adaptations

Biconcave shape to increase SA:V ratio, cytoplasm contains lots of haemoglobin, no nucleus, flexible to squeeze through narrow capillaries

Neutrophil function

Destroy pathogens by phagocytosis and secretion of enzymes

Neutrophil adaptation

Multi-lobed nucleus to get to site of infections, lots of lysosomes that contain enzymes to digest invading cells

Sperm cell function

Reproduction - to fuse with egg, initiate the development of an embryo and pass on fathers genes

Sperm cell adaptations

Haploid nucleus, acrosome in head contains digestive enzymes that can break down outer layer of egg cell, mid-piece packed with mitochondria to release energy for tail movement

Root hair cell function

Absorption of water and mineral ions from soil

Root hair cell adaptations

Root hair to increase SA so more uptake of water, thinner walls so water can move through easily, mitochondria for active transport of mineral ions

Ciliated epithelium function

Moving substances across the surface of a tissue

Ciliated epithelium adaptations

Cilia beat in a coordinated way to shift material along surface of tissue, goblet cells secrete mucus which helps to trap dirt/dust/microorganisms

Squamous epithelium function

Provide a surface covering or outer layer

Squamous epithelium adaptations

A single layer of flattened cells on a basement membrane, forming a thin cross section, shortening the diffusion pathway, permeable

Palisade cell function

Carry out photosynthesis to produce glucose and oxygen

Palisade cell adaptation

Large number of chloroplasts to maximise the absorption of light, tall and thin allowing light to penetrate deeper

Guard cell function

Control the opening of stomata to regulate water loss and gas exchange

Guard cell adaptation

Inner cell walls thicker/outer cell walls thinner to allow cell to bend when turgid, cytoplasm has high density of chloroplasts

Xylem tissue function

Transport tissue for water and dissolved ions

Xylem tissue adaptations

No top and bottom walls between cells to form continuous hollow tubes, cells are dead (free of organelles or cytoplasm) to allow free movement of water, outer walls thickened with lignin for support

Phloem tissue function

Transport of dissolved sugars and amino acids

Phloem tissue adaptations

Made of living cells supported by companion cells, cells are joined end to end and contain holes in the end cell walls which forms tubes, few sub cellular structures

Muscle tissue function

Contraction for movement

Muscle tissue adaptation

Layers of protein filaments which can slide over each other causing muscle contraction, high density of mitochondria

Cartilage function

To provide support

Cartilage adaptations

Strong and flexible tissue

What is a stem cell?

A cell that can divide by mitosis an unlimited number of times

What is potency?

The ability of cells to differentiate into more specialised cell types

Totipotent stem cells

Stem cells that can differentiate into any cell type found in an embryo, as well as extra-embryonic cells (cells that make up the placenta)

Pluripotent embryonic stem cells

Embryonic stem cells that can differentiate into any cell type found in an embryo but are not able to differentiate into extra-embryonic cells

Multipotent adult stem cells

Stem cells that can differentiate into a limited range of cell types

Adult stem cells function

Produce new cells for growth, cell replacement and tissue repair

Stem cell therapy

The introduction of adult stem cells into damaged tissue to treat diseases and injuries

What potency are stem cells found in bone marrow?

Multipotent (can only differentiate into erythrocytes, monocytes, neutrophils and lymphocytes)

What is a meristem?

Any undifferentiated tissue in a plant that has the ability to give rise to new cells

What is the cambium?

Tissue between xylem and phloem from which stem cells that form them originate

Which part of the cambium differentiates into xylem, and which into phloem cells?

Inner edge into xylem, outer edge into phloem

What happens to cambium cells that differentiate into xylem cells?

They lose their cytoplasm, deposit lignin in their cell walls and lose their end cell walls

What happens to cambium cells that differentiate into phloem cells?

They lose some of their cytoplasm and organelles and develop sieve plates (located at ends of cells)

What determines whether xylem or phloem tissue is produced from cambium?

The balance of different hormones

How many days after fertilisation are embryonic stem cells totipotent?

Up to 4 days

How many days after fertilisation do embryonic stem cells become pluripotent?

Day 5

Where are embryos used for research often sourced from?

The waste of embryos from in vitro fertilisation treatment

What are 3 examples of how stem cells can provide treatment for diseases/injuries?

Heart disease (when muscle tissue is damaged), Type 1 diabetes (patients have to inject insulin), treatment of burns

What is the main objection to using stem cells?

Religious objections - people belief life begins at conception and so destruction of embryos is murder

Why is the use of adult stem cells less controversial that embryonic stem cells?

The donor is able to give permission