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DAT > SNS Biology - Embryology > Flashcards

SNS Biology - Embryology Flashcards

1
Q

Development in Vertebrates
Fertilisation

A
  • Can occur 12-24 hrs after ovulation
  • Happens in lateral, widest portion of oviduct
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2
Q

Cleavage

A
  • Rapid mitotic divisions that occur shortly after fertilisation
  • Leads to an increase in cell number without corresponding growth in protoplasm (cell volume)
  • Also increases surface-to-volume ratio for each cell, improving gas and nutrient exchange
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3
Q

Cleavage
Indeterminate Cleavage

A
  • Cleavage that results in cells that maintain ability to develop into a complete organism
  • Identical twins are the result of determinate cleavage
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4
Q

Cleavage
Determinate Cleavage

A

• Cleavage resulting in cells whose future differentiation pathways are determined

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5
Q

Development in Vertebrates

A
  1. Fertilisation
  2. Cleavage
  3. Morula Formation
  4. Blastulation
  5. Gastrulation
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6
Q

Development in Vertebrates
Cleavage

A
  1. First complete cleavage of the zygote occurs ~32 hrs after fertilisation
  2. Second cleavage after 60 hrs
  3. Third cleavage after 72 hrs at which point the at which point the eigth celled embryo reaches the uterus
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7
Q

Development in Vertebrates
Morula Formation

A

As cell division continues, a solid ball of embryonic cells, the morula, is formed

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8
Q

Development in Vertebrates
Blastulation

A
  • Begins when the morula develops a fluid filled cavity called the blastocyst
  • By the fourth day, becomes a hollow sphere of cells called the blastula
  • At this stage the embryo adheres to the uterine wall
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9
Q

Development in Vertebrates
Gastrulation

A

• Once implanted in the uterus, cell migrations transform the single-cell layer of the blastocyst into a three layered structure called the gastrula

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10
Q

Development in Vertebrates
Types of Development

A
  1. External
  2. Internal non-placental
  3. Internal placental
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11
Q

Development in Vertebrates
Types of Development
External

A
  • Early development of many animals occurs outside of the mother’s body
  • For example fish and amphibians lay eggs that are fertilised externally. Reptiles and some mammals (duck billed platypus) develop externally on land
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12
Q

Development in Vertebrates
Types of Development
External
Embryonic Membranes

A
  1. Allantois
  2. Amnion
  3. Chorion
  4. Yolk Sac
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13
Q

Development in Vertebrates
Types of Development
External
Embryonic Membranes
Allantois

A

Sac-like structure involved in respiration and excretion. Contains blood vessels to transport O2, CO2, water, salt and nitrogenous waste

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14
Q

Development in Vertebrates
Types of Development
External
Embryonic Membranes
Amnion

A

Membrane enclosing amniotic fluid. Latter provides an aqueous environment that protects the developing embryo from shock

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15
Q

Development in Vertebrates
Types of Development
External
Embryonic Membranes
Chorion

A

Lines the inside of the shell. Moist membrane permitting gas exchange

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16
Q

Development in Vertebrates
Types of Development
External
Embryonic Membranes
Yolk Sac

A

Encloses the yolk. Blood vessels in the yolk sac transfer food to the developing embryo

17
Q

Development in Vertebrates
Types of Development
Internal Non-placental

A
  • Certain animals develop in the mother without a placenta
  • For example, marsupials, some tropical fish
  • Without a placenta, exchange of food and oxygen is limited
  • Offspring may be born very young
18
Q

Development in Vertebrates
Types of Development
Internal Placental

A
  • Growing foetus receives O2 directly from its mother via specialised circulatory system
  • Not only supplies O2 and nutrients, but removes CO2 and metabolic waste
  • Two key components are umbilical chord and placenta which both develop in the first few weeks after fertilisation
19
Q

Development in Vertebrates
Types of Development
Internal Placental
Development

A
  • Umbilical chord and placenta develop in the first few weeks after fertilisation
  • Outgrowths of the four extra-embryonic membranes formed during development – amnion, chorion, allantois and yolk sac
20
Q

Development in Vertebrates
Types of Development
Internal Placental
Development
Amnion

A

Thin, tough membrane containing amniotic fluid – shock absorber for external pressure and localised pressure during labour and childbirth

21
Q

Development in Vertebrates
Types of Development
Internal Placental
Development
Chorion

A

Membrane which completely surrounds the amnion

22
Q

Development in Vertebrates
Types of Development
Internal Placental
Development
Allantois

A

Membrane which develops as an outpocketing of the gut. Blood vessels of the allantoic wall enlarge and become the umbilical vessels which connect the foetus to the placenta

23
Q

Development in Vertebrates
Types of Development
Internal Placental
Development
Yolk Sac

A

Site of early development of blood vessels. Becomes associated with the umbilical vessels

24
Q

Development in Vertebrates
Birth
Labour

A

• Series of strong uterine contractions

  1. Three stages:
  2. Cervix thins and dilates, amniotic sac ruptures. Contractions mild
  3. Rapid contractions, birth of baby
  4. Uterus contracts, expelling the placenta and umbilical cord
25
Q

Plant Embryology
Seed Formation

A

Zygote divides mitotically to form the mass of cells called the embryo

26
Q

Plant Embryology
Seed Formation
Embryo Components

A
  1. Cotyledons – seed leaves. Dicots have two, monocots (grasses) have one
  2. Epicotyl – precursor of the upper stem and leaves
  3. Endosperm – grows and feeds the embryo. In dicots, the cotyledon absords the endosperm
  4. Hypocotyl – develops into the lower stem and root
  5. Seed coat – outer coating of the ovule. Embryo and seed coat together comprise the seed
27
Q

Plant Embryology
Seed Dispersal

A
  • Fruit in which most seeds develop is formed from the ovary walls, base of flower and other consolidated pistil components
  • Serves as means of dispersal, allowing to be carried by air, water or animals
28
Q

Plant Embryology
Plant Development

A
  • Growth in higher plants is restricted to the meristem (embryonic, undifferentiated) cells
  • Gradually, these elongate and differentiate into cells types characteristic of the species
29
Q

Plant Embryology
Plant Development
Apical Meristem

A

Found in the tips of roots and stems. Growth in length occurs only at these points

30
Q

Plant Embryology

Plant Development

Latersl Meristem

A
  • Or cambium
  • Located between the xylem and phloem.
  • Permits growth in diameter and can differentiate into new xylem and phloem cells
  • Not an active tissue in monocots (grasses) or herbaceous dicots (alfalfa) but is predominant in woody dicots (eg oaks)

DAT (53 decks)

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