Human, Animal, and Plant

Reproduction

Fertilization Fertilization is the fusion of a haploid sperm and

a haploid egg Produces a diploid zygote External fertilization occurs outside the

female’s body This is seen in fish and amphibians Because of the lack of protection and the harsh

environment, many eggs are released to ensure the species’ survival

Internal fertilization occurs inside the female’s reproductive tract

This is seen in birds, reptiles, and mammals

Embryonic Development After fertilization, the zygote begins to go through

mitosis rapidly The rapid mitotic divisions are called cleavage The zygote does not grow much in size, but

grows in cell number At first, cleavage creates a mass of cells called a

morula The morula becomes a ring of hundreds of cells

called a blastula

The center of the blastula is filled with a fluid, and is called the blastocoel

The blastula then goes through gastrulation, in which it becomes indented

The indented blastula is now called a gastrula, and has two layers

The outer layer is the ectoderm, and the inner layer is the endoderm

A third layer called the mesoderm forms between the ectoderm and the endoderm

The gastrula is now an embryo

Fertilization

egg

sperm

Cleavage starts

morulablastula

Gastrulation

gastrula

Embryo

ectoderm

mesoderm

endoderm

Differentiation In differentiation, the cells of the embryo

become specific body cells This is done by expressing certain genes and not

expressing others The ectoderm becomes the nervous system and

skin The mesoderm becomes the muscles, circulatory

system, skeleton, excretory system, and reproductive system

The endoderm becomes the lining of the digestive system and respiratory system, parts of the liver, and parts of the pancreas

Site of Development If fertilization was external, development will be

external Ex: fish embryos develop in the water Survival rate is very low, so many eggs are

fertilized The embryos’ food source is the yolk of the egg Birds and reptiles have internal fertilization, but

external development Their embryos feed on yolk as well

Their eggs have developed a shell for protection and membranes that provide a favorable environment for development

Embryonic membranes: 1. Amnion: contains the amniotic fluid that

provides a watery environment, protects the embryo from shock, and prevents the embryo from sticking to the shell

2. Yolk sac: surrounds the yolk and contains blood vessels that transport food to the embryo

3. Allantois: a respiratory membrane and a storage site for nitrogenous wastes like urea

4. Chorion: an outer membrane that surrounds the other membranes

Internal development occurs when the embryo grows inside of the body of the female

The parent provides nutrition and protection There is a relatively high survival rate, so fewer

eggs are fertilized

Placental Mammals Have internal fertilization and internal

development The embryo develops inside the uterus The eggs have very little yolk and are small

compared to the eggs of other animals The placenta forms inside the uterus from both

embryonic tissues and maternal tissues The placenta allows for the exchange of

nutrients, wastes, and respiratory gases between the mother and the embryo

The mother’s blood and the embryo’s blood never mix

Instead, materials are transported by diffusion and active transport

The umbilical cord, which contains blood vessels, connects the embryo to the placenta

Humans are placental mammals

Marsupials Marsupials are non-placental mammals Have internal fertilization and internal embryonic

development Nutrition for embryonic development does not

come directly from the mother The embryo lives off the yolk The embryo is born prematurely and completes

its development in the mother’s pouch The pouch contains the milk-producing

mammary glands

Human Gamete Production Human gametes are made in the gonads Testes in males Ovaries in females Male gametes are sperm Female gametes are eggs or ova Both gametes are made in meiosis Spermatogenesis is the production of sperm Oogenesis is the production of ova

In spermatogenesis, four sperm are made each time meiosis is done

In oogenesis, one ovum and three small polar bodies are made each time meiosis is done

The ovum is large enough to support embryonic growth

The polar bodies disintegrate

Male Reproductive System The testes are located in the scrotum outside

the body Sperm production occurs best at 1-2 degrees

below normal body temperature From the testes, the sperm move through tubes

called the vas deferens to the urethra The urethra is contained within the penis The penis allows for internal fertlization

The prostate gland, bulbourethral gland, and seminal vesicles produce liquid for the sperm as they travel through the vas deferens

The liquid makes semen, which nourishes the sperm and provides a watery environment for them to move through

The testes also produce the hormone testosterone

Testosterone regulates the maturation of sperm and the development of secondary sexual characteristics

Seminal vesicle

Vas deferens

Prostate gland

Bulbourethral gland

Penis

Urethra

Vas deferens

Epididymis

Testis

Scrotum

Female Reproductive System The ovaries produce ova in tiny cavities called

follicles The ovum is released from the ovary in ovulation

and enters one of the two Fallopian tubes (oviducts)

The uterus is where an embryo will develop The cervix is the opening of the uterus into the

vagina or birth canal

The ovaries produce the hormones estrogen and progesterone

These hormones regulate the menstrual cycle and the development of secondary sexual characteristics

Cervix

Vagina

Vaginal opening

Ovary

OviductUrinary bladder

Uterus

Urethra

Menstrual Cycle At birth, all the ova a female will ever produce

are already present in an immature form The menstrual cycle will begin at puberty and

stop at menopause The menstrual cycle is the rise and fall of

hormones that regulate the release of one ovum every 28 days

Also regulates the preparation of the uterus for pregnancy by thickening the lining of the uterus, called the endometrium

1. Follicle stage: the ovum matures in the ovary, and estrogen is releasedEstrogen causes the endometrium to thicken and

become more vascularized 2. Ovulation: the ovum is released from the

follicle and enters the Fallopian tubeMidpoint of the cycle = day 14

3. Corpus luteum stage: the empty follicle in the ovary becomes the corpus luteumThe corpus luteum releases progesterone, which

increases the thickening of the endometrium 4. Menstruation: the shedding of the

endometrium that occurs if fertilization does not take place

During the menstrual cycle, the hypothalamus in the brain and the pituitary gland also produce hormones

Follicle-stimulating hormone (FSH) causes follicle growth in the ovary and estrogen production

Estrogen production will eventually inhibit FSH Luteinizing hormone (LH) causes the growth of

the corpus luteum and the production of progesterone

Progesterone production will eventually inhibit estrogen, LH, and FSH

This regulation of hormones between the pituitary, hypothalamus, and ovaries is an example of negative feedback

releasesprogesterone

maintainsuteruslining

produces estrogen

LH

FSH

estrogen

progesterone

egg developmentovulation = egg release

corpus luteum

0 7 14 21 28days

Fertilization and Development Fertilization occurs in the upper one third of the

Fallopian tube If the ovum is not fertilized about 24 hours after

ovulation, it deteriorates If fertilization does occur, the zygote goes

through cleavage and travels to the uterusTakes about 6-10 days to reach the uterus

The zygote is an embryo by the time it reaches the uterus and has depleted its yolk supply

In the uterus, the embryo implants in the thick endometrium and can get nutrients from the mother

If more than one ovum was released and fertilized, fraternal twins developNo more alike than other siblings

If one zygote separates into two during cleavage, identical twins developHave the same DNA

In in vitro fertilization, the sperm and ovum are fused in the lab and then inserted into the mother’s uterusUsed when there is trouble conceiving naturally

Prenatal Development Cleavage occurs in the Fallopian tube Gastrulation occurs after the embryo has

implanted Differentiation and growth occur The placenta is the connection between mother

and embryo The amnion surrounds the embryo and contains

the amniotic fluid The umbilical cord holds the blood vessels that

carry materials between mother and embryo

7 weeks4 weeks

10 weeks

12 weeks 20 weeks

Prenatal development requires the supplying of a proper balance of nutrients to the embryo

Harmful substances like alcohol, tobacco smoke, drugs, and infections can travel through the placenta and harm the fetusCan lead to life-long health problems for the fetus

Birth Birth occurs after a nine-month gestation period Strong contractions of the uterus (labor) force the

baby through the cervix and vagina The placenta is forced out of the body after the

baby is delivered The mammary glands will provide milk for

nourishment and antibodies for immunity

Intestine

Placenta

Umbilicalcord

Wall ofuterus

VaginaCervix

Bladder

Asexual Plant Reproduction In vegetative propagation, a new plant grows out

of a part from an old plantSimilar to budding

People often cut stems from plants with desired traits and grow identical plants from those cuttings

Ex: a twig from an apple tree can be used to produce clones of the original tree

Parts of the Flower Meiosis and fertilization take place in the flower

of the plant The flower is specialized for sexual reproduction The male part of the flower is the stamen The female part of the flower is the pistil Flowers with both stamens and pistils are

complete flowers Flowers than have either stamens or pistils are

incomplete flowers

The stamen is made of the anther and the filament

The anther produces the haploid pollen grains The pistil is made of the stigma, style, and ovary The ovule that develops in the ovary contains the

haploid egg

Pollination Pollination is the transfer of pollen grains from

the anther to the stigma This can be done using the wind, insects, and

birds Colored petals and nectar attract pollinating

insects Self-pollination is the transfer of pollen from the

anther to the pistil of the same flower or same plant

Cross-pollination is the transfer of pollen from the anther of one plant to the pistil of another plant Increases genetic diversity

Pollen grains have thick walls to prevent dehydration as they travel

After pollination, the pollen grain germinates on the stigma and forms a pollen tube

The pollen tube travels down the stigma and into the ovule

Sperm nuclei are made and fuse with the egg

Embryo Development After fertilization, the ovule that contains the

embryo develops into a seed The seed is made of a seed coat and the embryo The ovary develops into a fruit The plant embryo has three parts: 1. Hypocotyl: becomes the root and the

lower stem 2. Epicotyl: becomes the leaves and the

upper stem

3. Cotyledons: contain stored food that will provide nutrition for the germinating plant

If a plant has one cotyledon, it is a monocot If a plant has two cotyledons, it is a dicot

Germination and Growth Seeds develop in fruit, which aid in seed

dispersal After dispersal, the seeds will germinate if the

conditions are rightSufficient moisture, proper temperature, and sufficient

oxygen After developing into a plant, growth continues at

the meristems Apical meristems are found at the tips of roots

and stems and cause an increase in length

Lateral meristems are found within the stem and cause the plant to grow wider

The meristems allow the plant to develop all its tissues and organs